du.sePublications
Change search
Refine search result
1234 101 - 150 of 151
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • chicago-author-date
  • chicago-note-bibliography
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics. Swedish University of Agricultural Sciences.
    The evolution of peer-reviewed papers.2019In: Journal of Animal Breeding and Genetics, ISSN 0931-2668, E-ISSN 1439-0388, Vol. 136, no 2, p. 77-78Article in journal (Other academic)
  • 102.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Al-Sarraj, Razaw
    von Rosen, Dietrich
    Non-iterative variance component estimation in QTL analysis.2009In: Journal of Animal Breeding and Genetics, ISSN 0931-2668, E-ISSN 1439-0388, Vol. 126, no 1, p. 110-116Article in journal (Refereed)
    Abstract [en]

    In variance component quantitative trait loci (QTL) analysis, a mixed model is used to detect the most likely chromosome position of a QTL. The putative QTL is included as a random effect and a method is needed to estimate the QTL variance. The standard estimation method used is an iterative method based on the restricted maximum likelihood (REML). In this paper, we present a novel non-iterative variance component estimation method. This method is based on Henderson's method 3, but relaxes the condition of unbiasedness. Two similar estimators were compared, which were developed from two different partitions of the sum of squares in Henderson's method 3. The approach was compared with REML on data from a European wild boar × domestic pig intercross. A meat quality trait was studied on chromosome 6 where a functional gene was known to be located. Both partitions resulted in estimated QTL variances close to the REML estimates. From the non-iterative estimates, we could also compute good approximations of the likelihood ratio curve on the studied chromosome.

  • 103.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Besnier, Francois
    Carlborg, Örjan
    Modelling dominance in a flexible intercross analysis2009In: BMC Genetics, ISSN 1471-2156, E-ISSN 1471-2156, Vol. 10, article id 30Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to develop a flexible model for analysis of quantitative trait loci (QTL) in outbred line crosses, which includes both additive and dominance effects. Our flexible intercross analysis (FIA) model accounts for QTL that are not fixed within founder lines and is based on the variance component framework. Genome scans with FIA are performed using a score statistic, which does not require variance component estimation.

    RESULTS: Simulations of a pedigree with 800 F2 individuals showed that the power of FIA including both additive and dominance effects was almost 50% for a QTL with equal allele frequencies in both lines with complete dominance and a moderate effect, whereas the power of a traditional regression model was equal to the chosen significance value of 5%. The power of FIA without dominance effects included in the model was close to those obtained for FIA with dominance for all simulated cases except for QTL with overdominant effects. A genome-wide linkage analysis of experimental data from an F2 intercross between Red Jungle Fowl and White Leghorn was performed with both additive and dominance effects included in FIA. The score values for chicken body weight at 200 days of age were similar to those obtained in FIA analysis without dominance.

    CONCLUSION: We have extended FIA to include QTL dominance effects. The power of FIA was superior, or similar, to standard regression methods for QTL effects with dominance. The difference in power for FIA with or without dominance is expected to be small as long as the QTL effects are not overdominant. We suggest that FIA with only additive effects should be the standard model to be used, especially since it is more computationally efficient.

  • 104.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Felleki, Majbritt
    Dalarna University, School of Technology and Business Studies, Statistics.
    Fikse, Freddy
    Mulder, Herman A.
    Strandberg, Erling
    Genetic heterogeneity of residual variance: estimation of variance components using double hierarchical generalized linear models2010In: Genetics Selection Evolution, ISSN 0999-193X, E-ISSN 1297-9686, Vol. 42, article id 8Article in journal (Refereed)
    Abstract [en]

    Background: The sensitivity to microenvironmental changes varies among animals and may be under genetic control. It is essential to take this element into account when aiming at breeding robust farm animals. Here, linear mixed models with genetic effects in the residual variance part of the model can be used. Such models have previously been fitted using EM and MCMC algorithms.

    Results: We propose the use of double hierarchical generalized linear models (DHGLM), where the squared residuals are assumed to be gamma distributed and the residual variance is fitted using a generalized linear model. The algorithm iterates between two sets of mixed model equations, one on the level of observations and one on the level of variances. The method was validated using simulations and also by re-analyzing a data set on pig litter size that was previously analyzed using a Bayesian approach. The pig litter size data contained 10,060 records from 4,149 sows. The DHGLM was implemented using the ASReml software and the algorithm converged within three minutes on a Linux server. The estimates were similar to those previously obtained using Bayesian methodology, especially the variance components in the residual variance part of the model.

    Conclusions: We have shown that variance components in the residual variance part of a linear mixed model can be estimated using a DHGLM approach. The method enables analyses of animal models with large numbers of observations. An important future development of the DHGLM methodology is to include the genetic correlation between the random effects in the mean and residual variance parts of the model as a parameter of the DHGLM.

  • 105.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics. Swedish Univ Agr Sci, Dept Anim Breeding & Genet, S-75007 Uppsala, Sweden.
    Felleki, Majbritt
    Dalarna University, School of Technology and Business Studies, Statistics. Swedish Univ Agr Sci, Dept Anim Breeding & Genet, S-75007 Uppsala, Sweden.
    Fikse, W. F.
    Mulder, H. A.
    Strandberg, E.
    Variance component and breeding value estimation for genetic heterogeneity of residual variance in Swedish Holstein dairy cattle2013In: Journal of Dairy Science, ISSN 0022-0302, E-ISSN 1525-3198, Vol. 96, no 4, p. 2627-2636Article in journal (Refereed)
    Abstract [en]

    Trait uniformity, or micro-environmental sensitivity, may be studied through individual differences in residual variance. These differences appear to be heritable, and the need exists, therefore, to fit models to predict breeding values explaining differences in residual variance. The aim of this paper is to estimate breeding values for micro-environmental sensitivity (vEBV) in milk yield and somatic cell score, and their associated variance components, on a large dairy cattle data set having more than 1.6 million records. Estimation of variance components, ordinary breeding values, and vEBV was performed using standard variance component estimation software (ASReml), applying the methodology for double hierarchical generalized linear models. Estimation using ASReml took less than 7 d on a Linux server. The genetic standard deviations for residual variance were 0.21 and 0.22 for somatic cell score and milk yield, respectively, which indicate moderate genetic variance for residual variance and imply that a standard deviation change in vEBV for one of these traits would alter the residual variance by 20%. This study shows that estimation of variance components, estimated breeding values and vEBV, is feasible for large dairy cattle data sets using standard variance component estimation software. The possibility to select for uniformity in Holstein dairy cattle based on these estimates is discussed.

  • 106.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics. Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Lee, Y
    Seoul National University, Seoul, Korea.
    Exploring the potential of hierarchical generalized linear models in animal breeding and genetics2013In: Journal of Animal Breeding and Genetics, ISSN 0931-2668, E-ISSN 1439-0388, Vol. 130, no 6, p. 415-416Article in journal (Refereed)
  • 107.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Lee, Youngjo
    Hierarchical generalized linear models have a great potential in genetics and animal breeding2010Conference paper (Refereed)
  • 108.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    McFarlane, S. Eryn
    Uppsala universitet.
    Husby, Arlid
    University of Helsinki; Norwegian University of Science and Technology.
    Kawakami, Takeshi
    Uppsala universitet.
    Ellegren, Hans
    Uppsala universitet.
    Qvarnström, Anna
    Uppsala universitet.
    Increasing the power of genome wide association studies in natural populations using repeated measures: evaluation and implementation2016In: Methods in Ecology and Evolution, ISSN 2041-210X, E-ISSN 2041-210X, Vol. 7, no 7, p. 792-799Article in journal (Refereed)
    Abstract [en]

    1. Genomewide association studies (GWAS) enable detailed dissections of the genetic basis for organisms' ability to adapt to a changing environment. In long-term studies of natural populations, individuals are often marked at one point in their life and then repeatedly recaptured. It is therefore essential that a method for GWAS includes the process of repeated sampling. In a GWAS, the effects of thousands of single-nucleotide polymorphisms (SNPs) need to be fitted and any model development is constrained by the computational requirements. A method is therefore required that can fit a highly hierarchical model and at the same time is computationally fast enough to be useful.

    2. Our method fits fixed SNP effects in a linear mixed model that can include both random polygenic effects and permanent environmental effects. In this way, the model can correct for population structure and model repeated measures. The covariance structure of the linear mixed model is first estimated and subsequently used in a generalized least squares setting to fit the SNP effects. The method was evaluated in a simulation study based on observed genotypes from a long-term study of collared flycatchers in Sweden.

    3. The method we present here was successful in estimating permanent environmental effects from simulated repeated measures data. Additionally, we found that especially for variable phenotypes having large variation between years, the repeated measurements model has a substantial increase in power compared to a model using average phenotypes as a response.

    4. The method is available in the R package RepeatABEL. It increases the power in GWAS having repeated measures, especially for long-term studies of natural populations, and the R implementation is expected to facilitate modelling of longitudinal data for studies of both animal and human populations.

  • 109.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rebreyend, Pascal
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Statistics.
    Vinterkonferens i rumslig statistik i Dalarna2011In: Qvintensen, ISSN 2000-1819, Vol. 2011, no 4Article in journal (Other academic)
  • 110.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Sand, Håkan
    Andren, Henrik
    Månsson, Johan
    Pehrson, Åke
    Evaluation of four methods used to estimate population density of moose (Alces alces)2008In: Wildlife Biology, ISSN 0909-6396, E-ISSN 1903-220X, Vol. 14, no 3, p. 358-371Article in journal (Refereed)
    Abstract [en]

    Various survey methods are used to monitor and manage ungulate popualations. The choice of optimal method depends on estimation accuracy, management objective and financial constraints. Here we compare estimates produced by four different methods for estimating population size, i.e. aerial counts, hunter observations, pellet group counts and cohort analysis. A Swedish moose Alces alces population was studied during 1973-2005 in the Grimso Wildlife Research Area (135 km(2)). The highest correlation was found between cohort analysis and aerial counts (r = 0.69. P < 0.05). and the hunter observations and the aerial counts (r = 0.76. P < 0.10). The different methods produced relatively consistent trends in population estimates over years. Pellet group counts prior to 1997 were not significantly correlated with the other methods. probably due to unrepresentative spatial sampling. A comparison of the aerial and pellet group counts in 2002 and 2006, showed that the average defecation rate was estimated at approximately 14 pellet groups per day per moose. Our results show the importance of having representative spatial sampling in pellet group surveys and indicate that hunter observations can be a useful tool for estimating long-term population trends even in moderately sized areas.

  • 111.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Shen, Xia
    Dalarna University, School of Technology and Business Studies, Statistics.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Hglm: A package for fitting hierarchical generalized linear models2010In: The R Journal, ISSN 2073-4859, E-ISSN 2073-4859, Vol. 2, no 2, p. 20-28Article in journal (Refereed)
    Abstract [en]

    We present the hglm package for fitting hierarchical generalized linear models. It can be used for linear mixed models and generalized linear mixed models with random effects for a variety of links and a variety of distributions for both the outcomes and the random effects. Fixed effects can also be fitted in the dispersion part of the model.

  • 112.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Valdar, William
    Detecting major genetic loci controlling phenotypic variability in experimental crosses2011In: Genetics, ISSN 0016-6731, E-ISSN 1943-2631, Vol. 188, no 2, p. 435-447Article in journal (Refereed)
    Abstract [en]

    Traditional methods for detecting genes that affect complex diseases in humans or animal models, milk production in livestock, or other traits of interest, have asked whether variation in genotype produces a change in that trait’s average value. But focusing on differences in the mean ignores differences in variability about that mean. The robustness, or uniformity, of an individual’s character is not only of great practical importance in medical genetics and food production but is also of scienti?c and evolutionary interest (e.g., blood pressure in animal models of heart disease, litter size in pigs, ?owering time in plants). We describe a method for detecting major genes controlling the phenotypic variance, referring to these as vQTL. Our method uses a double generalized linear model with linear predictors based on probabilities of line origin. We evaluate our method on simulated F2 and collaborative cross data, and on a real F2 intercross, demonstrating its accuracy and robustness to the presence of ordinary mean-controlling QTL. We also illustrate the connection between vQTL and QTL involved in epistasis, explaining how these concepts overlap. Our method can be applied to a wide range of commonly used experimental crosses and may be extended to genetic association more generally.

  • 113.
    Rönnegård, Lars
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Valdar, William
    Recent developments in statistical methods for detecting genetic loci affecting phenotypic variability2012In: BMC Genetics, ISSN 1471-2156, E-ISSN 1471-2156, Vol. 13, article id 63Article in journal (Refereed)
    Abstract [en]

    A number of recent works have introduced statistical methods for detecting genetic loci that affect phenotypic variability, which we refer to as variability-controlling quantitative trait loci (vQTL). These are genetic variants whose allelic state predicts how much phenotype values will vary about their expected means. Such loci are of great potential interest in both human and non-human genetic studies, one reason being that a detected vQTL could represent a previously undetected interaction with other genes or environmental factors. The simultaneous publication of these new methods in different journals has in many cases precluded opportunity for comparison. We survey some of these methods, the respective trade-offs they imply, and the connections between them. The methods fall into three main groups: classical non-parametric, fully parametric, and semi-parametric two-stage approximations. Choosing between alternatives involves balancing the need for robustness, flexibility, and speed. For each method, we identify important assumptions and limitations, including those of practical importance, such as their scope for including covariates and random effects. We show in simulations that both parametric methods and their semi-parametric approximations can give elevated false positive rates when they ignore mean-variance relationships intrinsic to the data generation process. We conclude that choice of method depends on the trait distribution, the need to include non-genetic covariates, and the population size and structure, coupled with a critical evaluation of how these fit with the assumptions of the statistical model.

  • 114.
    Saqlain, Murshid
    et al.
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Brandt, Daniel
    Dalarna University, School of Technology and Business Studies, Human Geography.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Westin, Jerker
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Stochastic differential equations modelling of levodopa concentration in patients with Parkinson's disease2018Conference paper (Other academic)
    Abstract [en]

    The purpose of this study is to investigate a pharmacokinetic model of levodopa concentration in patients with Parkinson's disease by introducing stochasticity so that inter-individual variability may be separated into measurement and system noise. It also aims to investigate whether the stochastic differential equations (SDE) model provide better fits than its ordinary differential equations (ODE) counterpart, by using a real data set. Westin et al. developed a pharmacokinetic-pharmacodynamic model for duodenal levodopa infusion described by four ODEs, the first three of which define the pharmacokinetic model. In this study, system noise variables are added to the aforementioned first three equations through a standard Wiener process, also known as Brownian motion. The R package PSM for mixed-effects models is used on data from previous studies for modelling levodopa concentration and parameter estimation. First, the diffusion scale parameter, σ, and bioavailability are estimated with the SDE model. Second, σ is fixed to integer values between 1 and 5, and bioavailability is estimated. Cross-validation is performed to determine whether the SDE based model explains the observed data better or not by comparingthe average root mean squared errors (RMSE) of predicted levodopa concentration. Both ODE and SDE models estimated bioavailability to be about 88%. The SDE model converged at different values of σ that were signicantly different from zero while estimating bioavailability to be about 88%. The average RMSE for the ODE model wasfound to be 0.2980, and the lowest average RMSE for the SDE model was 0.2748 when σ was xed to 4. Both models estimated similar values for bioavailability, and the non-zero σ estimate implies that the inter-individual variability may be separated. However, the improvement in the predictive performance of the SDE model turned out to be rather small, compared to the ODE model.

  • 115.
    Saras, Ulrika
    Dalarna University, School of Education and Humanities, Educational Work.
    ”Kunskaperna gömmer sig lite i roliga gubbar”: Pedagogers syn på iPadsanvändning som en del av matematikundervisningen i förskoleklass och årskurs 1-32013Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Syftet med detta arbete är att få kunskap om hur pedagoger i förskoleklass samt årskurserna 1-3 som har tillgång till iPads i sin matematikundervisning ser på användandet av dessa. Hur resonerar pedagoger när de använder iPadsen och finns det en tanke bakom hur iPadsen används när det gäller matematiska mål i Lgr 11? Metoden som användes för att få svar på frågeställningarna var dels en enkätundersökning för att nå ut till många pedagoger och därefter fördjupande intervjuer som baserade på enkätfrågornas resultat.

  • 116.
    Shen, Xia
    Dalarna University, School of Technology and Business Studies, Statistics.
    Novel Statistical Methods in Quantitative Genetics: Modeling Genetic Variance for Quantitative Trait Loci Mapping and Genomic Evaluation2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis develops and evaluates statistical methods for different types of genetic analyses, including quantitative trait loci (QTL) analysis, genome-wide association study (GWAS), and genomic evaluation. The main contribution of the thesis is to provide novel insights in modeling genetic variance, especially via random effects models.

    In variance component QTL analysis, a full likelihood model accounting for uncertainty in the identity-by-descent (IBD) matrix was developed. It was found to be able to correctly adjust the bias in genetic variance component estimation and gain power in QTL mapping in terms of precision. 

    Double hierarchical generalized linear models, and a non-iterative simplified version, were implemented and applied to fit data of an entire genome. These whole genome models were shown to have good performance in both QTL mapping and genomic prediction.

    A re-analysis of a publicly available GWAS data set identified significant loci in Arabidopsis that control phenotypic variance instead of mean, which validated the idea of variance-controlling genes. 

    The works in the thesis are accompanied by R packages available online, including a general statistical tool for fitting random effects models (hglm), an efficient generalized ridge regression for high-dimensional data (bigRR), a double-layer mixed model for genomic data analysis (iQTL), a stochastic IBD matrix calculator (MCIBD), a computational interface for QTL mapping (qtl.outbred), and a GWAS analysis tool for mapping variance-controlling loci (vGWAS).

  • 117. Shen, Xia
    et al.
    Li, Ying
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Uden, Peter
    Carlborg, Orjan
    Application of a genomic model for high-dimensional chemometric analysis2014In: Journal of Chemometrics, ISSN 0886-9383, E-ISSN 1099-128X, Vol. 28, no 7, p. 548-557Article in journal (Refereed)
    Abstract [en]

    The rapid development of newtechnologies for large-scale analysis of genetic variation in the genomes of individuals and populations has presented statistical geneticists with a grand challenge to develop efficient methods for identifying the small proportion of all identified genetic polymorphisms that have effects on traits of interest. To address such a "large p small n" problem, we have developed a heteroscedastic effects model (HEM) that has been shown to be powerful in high-throughput genetic analyses. Here, we describe how this whole-genome model can also be utilized in chemometric analysis. As a proof of concept, we use HEM to predict analyte concentrations in silage using Fourier transform infrared spectroscopy signals. The results show that HEM often outperforms the classic methods and in addition to this presents a substantial computational advantage in the analyses of such high-dimensional data. The results thus show the value of taking an interdisciplinary approach to chemometric analysis and indicate that large-scale genomic models can be a promising new approach for chemometric analysis that deserve to be evaluated more by experts in the field. The software used for our analyses is freely available as an R package at http://cran.r-project.org/web/packages/bigRR/. Copyright (C) 2014 JohnWiley & Sons, Ltd.

  • 118.
    Shen, Xia
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Estimation of Parameters in Random Effect Models with Incidence Matrix Uncertainty2010Conference paper (Other academic)
    Abstract [en]

    Random effect models have been widely applied in many fields of research. However, models with uncertain design matrices for random effects have been little investigated before. In some applications with such problems, an expectation method has been used for simplicity. This method does not include the extra information of uncertainty in the design matrix is not included. The closed solution for this problem is generally difficult to attain. We therefore propose an two-step algorithm for estimating the parameters, especially the variance components in the model. The implementation is based on Monte Carlo approximation and a Newton-Raphson-based EM algorithm. As an example, a simulated genetics dataset was analyzed. The results showed that the proportion of the total variance explained by the random effects was accurately estimated, which was highly underestimated by the expectation method. By introducing heuristic search and optimization methods, the algorithm can possibly be developed to infer the 'model-based' best design matrix and the corresponding best estimates.

  • 119.
    Shen, Xia
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carlborg, Örjan
    Hierarchical likelihood opens a new way of estimating genetic values using genome-wide dense marker maps2011In: BMC Proceedings, ISSN 1753-6561, E-ISSN 1753-6561, Proc. 14th European Workshop on QTL Mapping and Marker Assisted Selection (QTL-MAS), no 5(Suppl 3)Article in journal (Refereed)
    Abstract [en]

    Background Genome-wide dense markers have been used to detect genes and estimate relative genetic values. Among many methods, Bayesian techniques have been widely used and shown to be powerful in genome-wide breeding value estimation and association studies. However, computation is known to be intensive under the Bayesian framework, and specifying a prior distribution for each parameter is always required for Bayesian computation. We propose the use of hierarchical likelihood to solve such problems. Results Using double hierarchical generalized linear models, we analyzed the simulated dataset provided by the QTLMAS 2010 workshop. Marker-specific variances estimated by double hierarchical generalized linear models identified the QTL with large effects for both the quantitative and binary traits. The QTL positions were detected with very high accuracy. For young individuals without phenotypic records, the true and estimated breeding values had Pearson correlation of 0.60 for the quantitative trait and 0.72 for the binary trait, where the quantitative trait had a more complicated genetic architecture involving imprinting and epistatic QTL. Conclusions Hierarchical likelihood enables estimation of marker-specific variances under the likelihoodist framework. Double hierarchical generalized linear models are powerful in localizing major QTL and computationally fast.

  • 120.
    Shen, Xia
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carlborg, Örjan
    How to deal with genotype uncertainty in variance component quantitative trait loci analyses2011In: Genetics Research, ISSN 0016-6723, Vol. 93, no 5, p. 333-342Article in journal (Refereed)
    Abstract [en]

    Dealing with genotype uncertainty is an ongoing issue in genetic analyses of complex traits. Here we consider genotype uncertainty in quantitative trait loci (QTL) analyses for large crosses in variance component models, where the genetic information is included in identity-by-descent (IBD) matrices. An IBD matrix is one realization from a distribution of potential IBD matrices given available marker information. In QTL analyses, its expectation is normally used resulting in potentially reduced accuracy and loss of power. Previously, IBD distributions have been included in models for small human full-sib families. We develop an Expectation–Maximization (EM) algorithm for estimating a full model based on Monte Carlo imputation for applications in large animal pedigrees. Our simulations show that the bias of variance component estimates using traditional expected IBD matrix can be adjusted by accounting for the distribution and that the calculations are computationally feasible for large pedigrees.

  • 121. Shukur, Ghazi
    et al.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Framtida utmaningar för forskarutbildningen i statistik2013In: Qvintensen, ISSN 2000-1819, no 4, p. 21-21Article in journal (Other (popular science, discussion, etc.))
  • 122.
    Sjögren, Anna
    Dalarna University, School of Education and Humanities, Educational Work.
    "Vi ska bygga med långa klossar så att tornet blir ända upp till taket": En studie av verktyg och uttrycksformer när barn synliggör matematik i förskolans olika innomhusmiljöer2012Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Syftet med studien var att få kunskap om vilka verktyg och uttrycksformer barn använder när matematik synliggörs i den fria leken i förskolans olika inomhusmiljöer. Utgångspunkt har varit uttrycksformerna som finns beskrivna i förskolans läroplan (Lpfö 98, rev. 10) samt Bishops (1991) sex fundamentala matematiska aktiviteter. Följande frågeställningar användes:1.Genom vilka verktyg och uttrycksformer synliggörs olika matematikinnehåll? 2. Vilken matematik synliggörs i leken? 3. Vilka verktyg och uttrycksformer erbjuder miljön barnen?

    För att nå syftet och besvara frågeställningarna gjordes elva strukturerade observationer på barn 1 till 6 år med hjälp av observationsschema över barns fria lek. Fyra intervjuer med pedagoger genomfördes också. Tekniker som använts för observation och intervju är observationsschema, papper, penna, fotografering och ljudupptagning.

    Resultatet visar att uttrycksformen samtal, följd av rörelse samt bild och form, var vanligast förekommande när matematik synliggjordes i barns fria lek. Det verktyg som oftast förekom var att barnen använde kroppen som ett verktyg för samtal och rörelse. De konkreta material som främst användes som verktyg var spel och pussel, tätt följt av skapande- och konstruktions- material som t.ex. papper och pennor respektive klossar och duplo. Den matematik som synliggjordes var främst den matematiska aktiviteten konstruera då barnen sorterade, konstruerade och karakteriserade saker utifrån egenskaper. Konstruera följs av de matematiska aktiviteterna förklara och lokalisera där barnen har förklarat, argumenterat och dragit slutsatser respektive lokaliserat sig själva och olika figurer i olika rum. Det var oväntat att konstruera var den vanligaste aktiviteten då matematik ofta förknippas med att räkna. Detta resultat kan i detta fall kopplas till att miljön erbjuder mycket material som uppmuntrar denna matematiska aktivitet.

    En slutsats av undersökningen är att miljön har stor betydelse för vilka uttrycksformer barn får möjlighet att använda. De material barn väljer som verktyg, och som stimulerar till matematiska aktiviteter, är främst material som inte är matematiskt syftade.

  • 123.
    Snell, Charis
    Dalarna University, School of Education, Health and Social Studies, Mathematics Education.
    Programmering för matematisk problemlösning i årskurs 7-9: Hur hänger det ihop?2017Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Syftet med studien är att undersöka hur programmering för matematisk problemlösning kan integreras i matematikundervisning i årskurs 7-9. Skolverket har nyligen ändrat kursplanen för matematik så att programmering för matematisk problemlösning inkluderas i det centrala innehållet. För att undersöka syftet genomfördes studien i två delar. Lärare med programmeringskompetens intervjuades om hur de anser att programmering för matematisk problemlösning kan integreras i matematikundervisning. Två programmeringsverktyg undersöktes för att få svar på vilka möjligheter till arbete med matematisk problemlösning programmeringsverktyg erbjuder. Resultaten analyserades utifrån Bernsteins teori om klassifikation och inramning och visar att det finns många olika sätt att integrera programmering i matematikundervisning. Stora möjligheter finns för integrering av programmering för matematisk problemlösning med det centrala innehållet i kursplanen för matematik. Olika verktyg, uppgifter och arbetssätt erbjuder olika pedagogiska möjligheter.

  • 124.
    Snell, Charis
    Dalarna University, School of Education, Health and Social Studies, Mathematics Education.
    Programmering för problemlösning i matematik2017Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Syftet med studien är att undersöka hur deltagande i undervisning i programmering på grundskolan påverkar elevernas förmåga att lösa matematiska problem och att ta reda på vilka elevaktiviteter som används när programmeringsundervisningen som är kopplad till matematisk problemlösning genomförs. Studien genomfördes som en systematisk litteraturstudie vilket innebär att tidigare forskning har sökts igenom för att kunna besvara frågeställningarna. Resultaten visar att ämnet är komplext och att det är svårt att dra några tydliga slutsatser utifrån den forskning som finns om ämnet. Många studier är positiva till programmering som ett sätt för elever att formulera och lösa problem. Den största kvantitativa undersökningen finner dock inget bevis för att elever får en ökad problemlösningsförmåga genom arbete med programmering. Andra studier, som har undersökt både arbete med robotar och spelbyggande med skärmbaserade programmeringsspråk, beskriver hur elever får en mängd positiva effekter från arbete med programmering, som ökad förståelse av matematiska begrepp, ökad problemlösningsförmåga och ökad uthållighet och motivation. Elevaktiviteter som används inkluderar strukturerade problem, fria utforskningar, styrning av robotar, spelbyggande, kollaborativt arbete och att lära ut matematik till andra elever.

  • 125.
    Soltani Zamani, Ali
    Dalarna University, School of Education, Health and Social Studies, Educational Work.
    Gymnasieelevers möte med bokstavsymbolerna i algebra: Gymnasieelevers olika uppfattningar och svårigheter kring bokstavsymboler i algebra2017Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Det övergripande syftet med detta arbete är att ta reda på gymnasieelevers uppfattningar och missuppfattningar när de ska läsa, tolka och lösa uppgifter med algebraiska symboler. Arbetet fokuserar på elevernas svårigheter vilka upplevs olika i olika sammanhang såsom till exempel generalisering av tal, okänt tal och variabel. För att få svar på detta, intervjuades åtta gymnasieelever från olika årskurser och med skiftande algebrakunskaper. Resultatet blev att elever uppvisar olika svårigheter med algebraiska symboler, vilket stämmer överens med den forskning som är genomförd inom området. Detta ses som en följd av övergången från konkreta beräkningar i aritmetik till abstrakta och strukturerade beräkningar i algebra. Svårigheterna beror bland annat bero på att algebraiska symboler och tecken kan byta roll i ett algebraiskt uttryck medan elever brukar tolka dessa symboler endast ur en synvinkel. Elever ska därmed vara medvetna om symbolernas olika placeringar och dess egentliga innebörd. Slutsatsen banar då väg för lärare att arbeta utifrån olika utgångspunkter.

  • 126.
    Strand, Johanna
    Dalarna University, School of Education, Health and Social Studies, Mathematics Education.
    Gruppdiskussioner i problemlösning: En observations- och intervjustudie med fem verksamma lärare i matematik om lärarens roll vid gruppdiskussioner inom problemlösning för att utveckla ett matematiskt resonemang.2016Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Syftet med denna empiriska studie har varit att undersöka hur matematiklärare på högstadiet organiserar för och verkar för att utveckla elevers matematiska resonemang vid gruppdiskussioner inom problemlösning. För att svara på studiens syfte har en kvalitativ metod använts där intervjuer och observationer genomförts med fem verksamma lärare i matematik på högstadiet. Tidigare forskning visar att lärarens förmåga att skapa en god interaktion mellan lärare och elever samt elever till elever är en mycket viktig del för elevernas matematiska utveckling av resonemangsförmågan vilket resultatet visar att de verksamma lärarna möjliggör genom sin roll i gruppdiskussionen. Resultatet visar också att en god förberedelse inför gruppdiskussionen är lika viktig som själva genomförandet av den. Lärarna har också lyckats skapa ett didaktiskt kontrakt i klassrummen som svarar mot ett gynnande problemlösningsklassrum där elevernas matematiska förmågor och framförallt resonemangsförmågan ges möjlighet till utveckling. Av resultatet framgår att lärarna ännu inte funnit ett givande sätt för att få alla elever att aktivt delta i gruppdiskussionerna.

  • 127.
    Sumpter, Lovisa
    Umeå universitet, Institutionen för matematik och matematisk statistik.
    A reason to believe: beliefs as an influence on students task solving2008Report (Other academic)
    Abstract [en]

    Upper secondary students’ task solving reasoning was analysed, with a focus on what grounds they had for different strategy choices and conclusions. Beliefs were identified and connected with the reasoning that took place. The results indicate that beliefs have an impact on the central decisions made during task solving. Three themes stand out: safety, expectation and motivation.

  • 128.
    Sumpter, Lovisa
    Dalarna University, School of Education and Humanities, Mathematics Education.
    Myten om flickors osäkerhet2009In: Kvinnor och matematik : konferens den 14-16 juni 2009, Göteborg: konferensrapport / [ed] Berith Melander, Catarina Rudälv, Umeå: Institutionen för matematik och matematisk statistik, Umeå universitet , 2009, p. 83-84Conference paper (Other academic)
  • 129.
    Sumpter, Lovisa
    Umeå universitet, Institutionen för matematik och matematisk statistik.
    On Aspects of Mathematical Reasoning: Affect and Gender2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis explores two aspects of mathematical reasoning: affect and gender. I started by looking at the reasoning of upper secondary students when solving tasks. This work revealed that when not guided by an interviewer, algorithmic reasoning, based on memorising algorithms which may or may not be appropriate for the task, was predominant in the students reasoning. Given this lack of mathematical grounding in students reasoning I looked in a second study at what grounds they had for different strategy choices and conclusions. This qualitative study suggested that beliefs about safety, expectation and motivation were important in the central decisions made during task solving.  But are reasoning and beliefs gendered? The third study explored upper secondary school teachers conceptions about gender and students mathematical reasoning. In this study I found that upper secondary school teachers attributed gender symbols including insecurity, use of standard methods and imitative reasoning to girls and symbols such as multiple strategies especially on the calculator, guessing and chance-taking were assigned to boys. In the fourth and final study I found that students, both male and female, shared their teachers view of rather traditional feminities and masculinities. Remarkably however, this result did not repeat itself when students were asked to reflect on their own behaviour: there were some discrepancies between the traits the students ascribed as gender different and the traits they ascribed to themselves. Taken together the thesis suggests that, contrary to conceptions, girls and boys share many of the same core beliefs about mathematics, but much work is still needed if we should create learning environments that provide better opportunities for students to develop beliefs that guide them towards well-grounded mathematical reasoning. 

  • 130.
    Sumpter, Lovisa
    Umeå universitet, Institutionen för matematik och matematisk statistik.
    Teachers' conceptions about students' mathematical reasoning: Gendered or not?2009Report (Other academic)
    Abstract [en]

    This study looks at how upper secondary school teachers gender stereotype aspects of students' mathematical reasoning. Girls were attributed gender symbols including insecurity, use of standard methods and imitative reasoning. Boys were assigned the symbols such as multiple strategies especially on the calculator, guessing and chance-taking. 

  • 131.
    Sumpter, Lovisa
    Umeå universitet, Institutionen för matematik och matematisk statistik.
    Upper secondary school students' gendered conceptions about mathematics2009Report (Other academic)
    Abstract [en]

    This study explores Swedish Natural Science students' conceptions about gender and mathematics. I conducted and compared the results from two questionnaires. The first questionnaire revealed a view of rather traditional feminities and masulinities, a result that did not repeat itself in the second questionnaire. There was a discrepancy between the traits the students ascribed as gender different and the traits they ascribed to themselves.

  • 132.
    Sundberg, Rikard
    Dalarna University, School of Education, Health and Social Studies, Educational Work.
    Digital teknik i geometriundervisningen i årskurs 4-6.: Hur den digitala tekniken kan användas av läraren och eleverna, dess effekter, samt de möjligheter och hinder som finns med densamma.2017Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Digital teknik finns i den svenska skolan, men används inte alltid inom matematikundervisningen. Elevers resultat i geometri har tidigare varit låga i olika internationella undersökningar. Det finns programvaror särskilt framtagna för geometriundervisning. I den här litteraturstudien undersöks på vilka sätt digital teknik kan användas för att lyfta fram det matematiska innehållet i geometriundervisningen i grundskolans årskurs 4-6 samt vilken effekt användandet kan ha på resultatet. Även vilka möjligheter och hinder som finns med digital teknik i geometriundervisningen undersöks. Det visar sig att digital teknik kan användas på flera sätt och att användandet har en positiv effekt på resultatet. Möjligheterna är många då digital teknik finns tillgänglig och sätten den kan nyttjas går att variera. Studien visar även att ett av de större hindren är lärares digitala kompetens.

  • 133.
    Svenson, Kristin
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    A Microdata Analysis Approach to Transport Infrastructure Maintenance2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Maintenance of transport infrastructure assets is widely advocated as the key in minimizing current and future costs of the transportation network. While effective maintenance decisions are often a result of engineering skills and practical knowledge, efficient decisions must also account for the net result over an asset's life-cycle. One essential aspect in the long term perspective of transport infrastructure maintenance is to proactively estimate maintenance needs. In dealing with immediate maintenance actions, support tools that can prioritize potential maintenance candidates are important to obtain an efficient maintenance strategy.

    This dissertation consists of five individual research papers presenting a microdata analysis approach to transport infrastructure maintenance. Microdata analysis is a multidisciplinary field in which large quantities of data is collected, analyzed, and interpreted to improve decision-making. Increased access to transport infrastructure data enables a deeper understanding of causal effects and a possibility to make predictions of future outcomes. The microdata analysis approach covers the complete process from data collection to actual decisions and is therefore well suited for the task of improving efficiency in transport infrastructure maintenance.

    Statistical modeling was the selected analysis method in this dissertation and provided solutions to the different problems presented in each of the five papers. In Paper I, a time-to-event model was used to estimate remaining road pavement lifetimes in Sweden. In Paper II, an extension of the model in Paper I assessed the impact of latent variables on road lifetimes; displaying the sections in a road network that are weaker due to e.g. subsoil conditions or undetected heavy traffic. The study in Paper III incorporated a probabilistic parametric distribution as a representation of road lifetimes into an equation for the marginal cost of road wear. Differentiated road wear marginal costs for heavy and light vehicles are an important information basis for decisions regarding vehicle miles traveled (VMT) taxation policies.

    In Paper IV, a distribution based clustering method was used to distinguish between road segments that are deteriorating and road segments that have a stationary road condition. Within railway networks, temporary speed restrictions are often imposed because of maintenance and must be addressed in order to keep punctuality. The study in Paper V evaluated the empirical effect on running time of speed restrictions on a Norwegian railway line using a generalized linear mixed model.

  • 134.
    Svenson, Kristin
    Dalarna University, School of Technology and Business Studies, Statistics.
    Estimated lifetimes of road pavements in Sweden using time-to-event analysis2014In: Journal of transportation engineering, ISSN 0733-947X, E-ISSN 1943-5436, Vol. 140, no 11, article id 04014056Article in journal (Refereed)
    Abstract [en]

    Maintenance planning of road pavement requires reliable estimates of roads' lifetimes. In determining the lifetime of a road, this study combines maintenance activities and road condition measurements. The scope of the paper is to estimate lifetimes of road pavements in Sweden with time-to-event analysis. The model is stratified according to traffic load and includes effects of pavement type, road type, bearing capacity, road width, speed limit, stone size, and climate zone. Among the nine analyzed pavement types, stone mastic had the longest expected lifetime with a hazard ratio (risk of needing maintenance) estimated to be 36% lower than asphalt concrete. Among road types, 2+1 roads had 22% higher hazard ratio than ordinary roads indicating significantly lower lifetimes. Increased speed lowered the lifetime, while increased stone size (up to 20 mm) and increased road width lengthened the lifetime. The results are of importance for life-cycle cost analysis and road management. (C) 2014 American Society of Civil Engineers.

  • 135.
    Svenson, Kristin
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Li, Yujiao
    Dalarna University, School of Technology and Business Studies, Statistics.
    Macuchova, Zuzana
    Dalarna University, School of Technology and Business Studies, Human Geography.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Evaluating needs of road maintenance in Sweden with the mixed proportional hazards model2016In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2589, p. 51-58Article in journal (Refereed)
    Abstract [en]

    National road databases often lack important information for long-term maintenance planning of paved roads. In the Swedish case, latent variables of which there are no recordings in the pavement management systems database are, for example, underlying road construction, subsoil conditions, and amount of heavy traffic measured by the equivalent single-axle load. The mixed proportional hazards model with random effects was used to capture the effect of these latent variables on a road's risk of needing maintenance. Estimation of random effects makes it possible to identify sections that have shorter or longer lifetimes than could be expected from the observed explanatory variables (traffic load, pavement type, road type, climate zone, road width, speed limit, and bearing capacity restrictions). The results indicate that the mixed proportional hazards model is useful for maintenance planning because the weakest and strongest sections in a road network can be identified. The effect of the latent variables was visualized by,plotting the random effect of each section in a map of the road network. In addition, the spatial correlation between road sections was evaluated by fitting the random effects in an intrinsic conditional autoregressive model. The spatial correlation was estimated to explain 17% of the variation in lifetimes of roads that occur because of the latent variables. The Swedish example shows that the mixed proportional hazards and intrinsic conditional autoregressive models are suitable for analyzing the effect of latent variables in national road databases.

  • 136.
    Svenson, Kristin
    et al.
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    McRobbie, S.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Detecting road pavement deterioration with finite mixture models2019In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 20, no 4, p. 458-465Article in journal (Refereed)
    Abstract [en]

    Budget restrictions often limit the number of possible maintenance activities in a road network each year. To effectively allocate resources, the rate of road pavement deterioration is of great importance. If two maintenance candidates have an equivalent condition, it is reasonable to maintain the segment with the highest deterioration rate first. To identify such segments, finite mixture models were applied to road condition data from a part of the M4 highway in England. Assuming that data originates from two different normal distributions – defined as a ‘change’ distribution and an ‘unchanged’ distribution – all road segments were classified into one of the groups. Comparisons with known measurement errors and maintenance records showed that segments in the unchanged group had a stationary road condition. Segments classified into the change group showed either a rapid deterioration, improvement in condition because of previous maintenance or unusual measurement errors. Together with additional information from maintenance records, finite mixture models can identify segments with the most rapid deterioration rate, and contribute to more efficient maintenance decisions.

  • 137.
    Thomas, Ilias
    et al.
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Bergquist, Filip
    Johansson, Dongni
    Memedi, Mevludin
    Nyholm, Dag
    Westin, Jerker
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Sensor-based algorithmic dosing suggestions for oral administration of levodopa/carbidopa microtablets for Parkinson's disease: a first experience2019In: Journal of Neurology, ISSN 0340-5354, E-ISSN 1432-1459, Vol. 266, no 3, p. 651-658Article in journal (Refereed)
    Abstract [en]

    OBJECTIVE: Dosing schedules for oral levodopa in advanced stages of Parkinson's disease (PD) require careful tailoring to fit the needs of each patient. This study proposes a dosing algorithm for oral administration of levodopa and evaluates its integration into a sensor-based dosing system (SBDS).

    MATERIALS AND METHODS: In collaboration with two movement disorder experts a knowledge-driven, simulation based algorithm was designed and integrated into a SBDS. The SBDS uses data from wearable sensors to fit individual patient models, which are then used as input to the dosing algorithm. To access the feasibility of using the SBDS in clinical practice its performance was evaluated during a clinical experiment where dosing optimization of oral levodopa was explored. The supervising neurologist made dosing adjustments based on data from the Parkinson's KinetiGraph™ (PKG) that the patients wore for a week in a free living setting. The dosing suggestions of the SBDS were compared with the PKG-guided adjustments.

    RESULTS: The SBDS maintenance and morning dosing suggestions had a Pearson's correlation of 0.80 and 0.95 (with mean relative errors of 21% and 12.5%), to the PKG-guided dosing adjustments. Paired t test indicated no statistical differences between the algorithmic suggestions and the clinician's adjustments.

    CONCLUSION: This study shows that it is possible to use algorithmic sensor-based dosing adjustments to optimize treatment with oral medication for PD patients.

  • 138.
    Thomas, Ilias
    et al.
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    Memedi, Mevludin
    Westin, Jerker
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Nyholm, Dag
    The effect of continuous levodopa treatment during the afternoon hours2019In: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 139, no 1, p. 70-75Article in journal (Refereed)
    Abstract [en]

    OBJECTIVE: The aim of this retrospective study was to investigate if patients with PD, who are treated with levodopa-carbidopa intestinal gel (LCIG), clinically worsen during the afternoon hours and if so, to evaluate whether this occurs in all LCIG-treated patients or in a sub-group of patients.

    METHODS: Three published studies were identified and included in the analysis. All studies provided individual response data assessed on the treatment response scale (TRS) and patients were treated with continuous LCIG. Ninety-eight patients from the three studies fulfilled the criteria. T-tests were performed to find differences on the TRS values between the morning and the afternoon hours, linear mixed effect models were fitted on the afternoon hours' evaluations to find trends of wearing-off, and patients were classified into three TRS categories (meaningful increase in TRS, meaningful decrease in TRS, non -meaningful increase or decrease).

    RESULTS: In all three studies significant statistical differences were found between the morning TRS values and the afternoon TRS values (p-value <= 0.001 in all studies). The linear mixed effect models had significant negative coefficients for time in two studies, and 48 out of 98 patients (49%) showed a meaningful decrease of TRS during the afternoon hours.

    CONCLUSION: The results from all studies were consistent, both in the proportion of patients in the three groups and the value of TRS decrease in the afternoon hours. Based on these findings there seems to be a group of patients with predictable "off" behavior in the later parts of the day. This article is protected by copyright. All rights reserved.

  • 139.
    Tingbratt, Emma
    Dalarna University, School of Education, Health and Social Studies, Mathematics Education.
    Vad är algebra och vad ska man ha det till?: En studie av några högstadieelevers uppfattningar om algebra2014Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
  • 140.
    Valyukh, Iryna
    Dalarna University, School of Technology and Business Studies, Materials Technology. Uppsala universitet, Institutionen för teknikvetenskaper.
    Optical Characterization and Optimization of Display Components: Some Applications to Liquid-Crystal-Based and Electrochromics-Based Devices2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This dissertation is focused on theoretical and experimental studies of optical properties of materials and multilayer structures composing liquid crystal displays (LCDs) and electrochromic (EC) devices.

    By applying spectroscopic ellipsometry, we have determined the optical constants of thin films of electrochromic tungsten oxide (WOx) and nickel oxide (NiOy), the films’ thickness and roughness. These films, which were obtained at spattering conditions possess high transmittance that is important for achieving good visibility and high contrast in an EC device.

    Another application of the general spectroscopic ellipsometry relates to the study of a photo-alignment layer of a mixture of azo-dyes SD-1 and SDA-2. We have found the optical constants of this mixture before and after illuminating it by polarized UV light. The results obtained confirm the diffusion model to explain the formation of the photo-induced order in azo-dye films.

    We have developed new techniques for fast characterization of twisted nematic LC cells in transmissive and reflective modes. Our techniques are based on the characteristics functions that we have introduced for determination of parameters of non-uniform birefringent media. These characteristic functions are found by simple procedures and can be utilised for simultaneous determination of retardation, its wavelength dispersion, and twist angle, as well as for solving associated optimization problems.

    Cholesteric LCD that possesses some unique properties, such as bistability and good selective scattering, however, has a disadvantage – relatively high driving voltage (tens of volts). The way we propose to reduce the driving voltage consists of applying a stack of thin (~1µm) LC layers.

    We have studied the ability of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. We have demonstrated that in order to accomplish good color characteristics and high brightness of the display, one or two retardation plates are sufficient.

  • 141.
    Virtanen, Susanna
    Dalarna University, School of Education and Humanities, Educational Work.
    Elevers möjlighet till reflektion i matematikundervisningen: En studie i grunskolans årskurs 92013Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Research presented in the literature study show the significant value of reflection in the learning process. The overview also highlights activities that encourage and inhibit students’ reflection. The aim of this study is to examine whether and how students in Swedish school, grade 9, are stimulated to use reflection in mathematics education. This was conducted through a qualitative study, with essentially lesson observations as the main method and teacher interviews as supporting method. Teaching activities that may have a positive or negative effect on students’ ability to reflect have been identified in the process and analysis of the research material and are presented in the result chapter. The results show that although teachers express a positive view on metacognition and reflective approach, such situations occur to a limited extent. Common in teachers’ lessons are sequences that could stimulate reflection if appropriate actions as follow up had been taken. The result of the study could make teachers aware of what kind of activities that support reflection. It may also convey the importance of the fact that pupils need to be taught and subjected to a teaching practice that continually requires the presence of reflection.

  • 142. Wang, Yu
    et al.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Nääs, Ola
    Dalarna University, School of Technology and Business Studies, Statistics.
    Är kommunala sommarjobb en gräddfil till arbetsmarknaden?2006Report (Other academic)
  • 143.
    Wikström, Daniel
    Dalarna University, School of Technology and Business Studies, Statistics.
    A Note on Proxy Variables and Instrument Variable Regression2015Report (Other academic)
    Abstract [en]

    This is a note about proxy variables and instruments for identification of structural parameters in regression models. We have experienced that in the econometric textbooks these two issues are treated separately, although in practice these two concepts are very often combined. Usually, proxy variables are inserted in instrument variable regressions with the motivation they are exogenous. Implicitly meaning they are exogenous in a reduced form model and not in a structural model. Actually if these variables are exogenous they should be redundant in the structural model, e.g. IQ as a proxy for ability. Valid proxies reduce unexplained variation and increases the efficiency of the estimator of the structural parameter of interest. This is especially important in situations when the instrument is weak. With a simple example we demonstrate what is required of a proxy and an instrument when they are combined. It turns out that when a researcher has a valid instrument the requirements on the proxy variable is weaker than if no such instrument exists

  • 144.
    Wikström, Daniel
    Dalarna University, School of Technology and Business Studies, Statistics.
    Consistent method of moments estimation of the true fixed effects model2015Report (Other academic)
  • 145.
    Wikström, Daniel
    Dalarna University, School of Technology and Business Studies, Statistics.
    Consistent method of moments estimation of the true fixed effects model2015In: Economics Letters, ISSN 0165-1765, E-ISSN 1873-7374, Vol. 137, p. 62-69Article in journal (Refereed)
    Abstract [en]

    About a decade ago William H. Greene introduced the so-called ‘True fixed effects’ (TFE) model, which is intended to discriminate between heterogeneity and efficiency in stochastic frontier analysis. We would say that the TFE model has had a huge impact on applied stochastic frontier analysis. One problem with the original TFE estimator, is its inconsistency in cases with finite time observations, at least for the variance components. For the normal-half-normal model, this problem was solved by Chen et al. (2014) based on maximum likelihood estimation of the within-transformed model. In this study, we illustrate the possibilities offered by method of moments estimation. This approach is more flexible than the MLE proposed by Chen et al. (2014), since the method of moments estimators are not so closely dependent on the distributional assumptions and do not hinge on an explicit distribution of the random error. We only assume symmetry, as well as a fixed fourth-order cumulant for more complicated models. Greene’s methodology can, and has been, generalized to other models than the normal-half-normal model. However, the method of moments estimators proposed here are consistent.

  • 146.
    Wikström, Daniel
    Dalarna University, School of Technology and Business Studies, Statistics.
    The true fixed effects model with non-stationary inefficiency distribution2015Report (Other academic)
  • 147.
    Yella, Siril
    et al.
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Nyberg, Roger G
    Dalarna University, School of Technology and Business Studies, Information Systems.
    Gupta, Narendra K.
    Edinburgh Napier University.
    Dougherty, Mark
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Reliability of manual assessments in determining the types of vegetation on railway tracks2015In: Web Information Systems Engineering – WISE 2015: 16th International Conference, Miami, FL, USA, November 1-3, 2015, Proceedings, Part II / [ed] Wang, J., Cellary, W., Wang, D., Wang, H., Chen, S.-C., Li, T., Zhang, Y., Springer, 2015, Vol. 9149, p. 391-399Conference paper (Refereed)
    Abstract [en]

    Current day vegetation assessments within railway maintenance are (to a large extent) carried out manually. This study has investigated the reliability of such manual assessments by taking three non-domain experts into account. Thirty-five track images under different conditions were acquired for the purpose. For each image, the raters’ were asked to estimate the cover of woody plants, herbs and grass separately (in %) using methods such as aerial canopy cover, aerial foliar cover and sub-plot frequency. Visual estimates of raters’ were recorded and analysis-of-variance tests on the mean cover estimates were investigated to see whether if there were disagreements between the raters’.  In tra-correl ation coefficient was used to study the differences between the estimates. Results achieved in this work revealed that seven out of the nine analysis-of-variance tests conducted in this study have demonstrated significant difference in the mean estimates of cover (p < 0.05).

  • 148.
    Youngjo, Lee
    et al.
    Seoul National University.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Noh, Maengseok
    Pukyong National University, Korea.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Skarin, Anna
    Swedish University of Agricultural Science, Uppsala.
    Spatial modeling of data with excessive zeros applied to reindeer pellet-group counts2016In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 6, no 19, p. 7047-7056Article in journal (Refereed)
    Abstract [en]

    We analyze a real data set pertaining to reindeer fecal pellet-group counts obtained from a survey conducted in a forest area in northern Sweden. In the data set, over 70% of counts are zeros, and there is high spatial correlation. We use conditionally autoregressive random effects for modeling of spatial correlation in a Poisson generalized linear mixed model (GLMM), quasi-Poisson hierarchical generalized linear model (HGLM), zero-inflated Poisson (ZIP), and hurdle models. The quasi-Poisson HGLM allows for both under- and overdispersion with excessive zeros, while the ZIP and hurdle models allow only for overdispersion. In analyzing the real data set, we see that the quasi-Poisson HGLMs can perform better than the other commonly used models, for example, ordinary Poisson HGLMs, spatial ZIP, and spatial hurdle models, and that the underdispersed Poisson HGLMs with spatial correlation fit the reindeer data best. We develop R codes for fitting these models using a unified algorithm for the HGLMs. Spatial count response with an extremely high proportion of zeros, and underdispersion can be successfully modeled using the quasi-Poisson HGLM with spatial random effects.

  • 149.
    Zhao, Xiaoyun
    Dalarna University, School of Technology and Business Studies, Statistics.
    On processing GPS tracking data of spatio-temporal car movements: a case study2015In: Journal of Location Based Services, ISSN 1748-9725, Vol. 9, no 4, p. 235-253Article in journal (Refereed)
    Abstract [en]

    The advancement of GPS technology has made it possible to use GPS devices as orientation and navigation tools, but also as tools to track spatio-temporal information. GPS tracking data can be broadly applied in location-based services, such as spatial distribution of the economy, transportation routing and planning, traffic management and environmental control. Therefore, knowledge of how to process the data from a standard GPS device is crucial for further use. Previous studies have considered various issues of the data processing at the time. This paper, however, aims to outline a general procedure for processing GPS tracking data. The procedure is illustrated step by step by the processing of real-world GPS data of car movements in Borlänge in the centre of Sweden. 

  • 150.
    Zhao, Xiaoyun
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Dan, Zhiguang
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Information Systems. Dalarna University, School of Technology and Business Studies, Human Geography.
    Network density and the p-median solution2013Report (Other academic)
    Abstract [en]

    The p-medianmodel is commonly used to find optimal locations of facilities for geographically distributed demands. So far, there are few studies that have considered the importance of the road network in the model. However, Han, Håkansson, and Rebreyend (2013) examined the solutions of the p-median model with densities of the road network varying from 500 to 70,000 nodes. They found as the density went beyond some 10,000 nodes, solutions have no further improvements but gradually worsen. The aim of this study is to check their findings by using an alternative heuristic being vertex substitution, as a complement to their using simulated annealing. We reject the findings in Han et al (2013). The solutions do not further improve as the nodes exceed 10,000, but neither do the solutions deteriorate.

1234 101 - 150 of 151
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • chicago-author-date
  • chicago-note-bibliography
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf