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  • 1.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    An efficient algorithm for the pseudo likelihood estimation of the generalized linear mixed models (GLMM) with correlated random effects2009Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a two-step pseudo likelihood estimation technique for generalized linear mixed models with correlated random effects. The proposed estimation technique does not require reparametarisation of the model. Multivariate Taylor's approximation has been used to approximate the intractable integrals in the likelihood function of the GLMM. Based on the analytical expression for the estimator of the covariance matrix of the random effects, a condition has been presented as to when such a covariance matrix can be estimated through the estimates of the random effects. An application of the model with a binary response variable has been presented using a real data set on credit defaults from two Swedish banks. Due to the use of two-step estimation technique, proposed algorithm outperforms the conventional pseudo likelihood algorithms in terms of computational time.

  • 2.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    An efficient estimation of the GLMM with correlated random effects2008Ingår i: COMPSTAT'2008: International Conference on Computational Statistics / [ed] Moudud, Alam, Porto-Portugal, 2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a two-step pseudo likelihood estimation technique for the generalized linear mixed models (GLMM) with random effects being correlated (possibly between subjects). Due to the use of the two-step estimation technique the proposed algorithm outperforms the conventional pseudo likelihood algorithms, e.g. Wolfinger and O’Connell (1993), in terms of computational time. Moreover, it does not require any reparametarisation of the model such as Lindstrom and Bates (1989). Multivariate Taylor’s approximation has been used to approximate the intractable integrals in the likelihood function of the GLMM. Based on the analytical expression for the estimator of the covariance matrix of the random effects, a condition has been presented as to when such a covariance matrix can be estimated through the estimates of the random effects. An application of the estimation technique with a binary response variable is presented using a real data set on credit defaults.

  • 3.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Feasible computation of the generalized linear mixed models with application to credit risk modelling2010Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    This thesis deals with developing and testing feasible computational procedures to facilitate the estimation of and carry out the prediction with the generalized linear mixed model (GLMM) with a scope of applying them to large data sets. The work of this thesis is motivated from an issue arising in credit risk modelling. We have access to a huge data set, consisting of about one million observations, on credit history obtained from two major Swedish banks. The principal research interest involved with the data analysis is to model the probability of credit defaults by incorporating the systematic dependencies among the default events. In order to model the dependent credit defaults we adopt the framework of GLMM which is a popular approach to model correlated binary data. However, existing computational procedures for GLMM did not offer us the flexibility to incorporate the desired correlation structure of defaults events. For the feasible estimation of the GLMM we propose two estimation techniques being the fixed effects (FE) approach and the two-step pseudo likelihood approach (2PL). The preciseness of the estimation techniques and their computational advantages are studied by Monte-Carlo simulations and by applying them to the credit risk modelling. Regarding the prediction issue, we show how to apply the likelihood principle to carry out prediction with GLMM. We also provide an R add-in package to facilitate the predictive inference for GLMM.

  • 4.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Feasible estimation of generalized linear mixed models (GLMM) with weak dependency between groups2010Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    This paper presents a two-step pseudo likelihood estimation technique for generalized linear mixed models with the random effects being correlated between groups. The core idea is to deal with the intractable integrals in the likelihood function by multivariate Taylor's approximation. The accuracy of the estimation technique is assessed in a Monte-Carlo study. An application of it with a binary response variable is presented using a real data set on credit defaults from two Swedish banks. Thanks to the use of two-step estimation technique, the proposed algorithm outperforms conventional pseudo likelihood algorithms in terms of computational time.

  • 5.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Industry shocks and empirical evidences on defaults comovement2009Rapport (Övrigt vetenskapligt)
    Abstract [en]

    It is commonly agreed that the credit defaults are correlated. However, the mechanism of such dependence is not yet fully understood. This paper contributes to the current understanding about the defaults comovement in the following way. Assuming that the industries provides the basis of defaults comovement it provides empirical evidence as to how such comovements can be modeled using correlated industry shocks. Generalized linear mixed model (GLMM) with correlated random effects is used to model the defaults comovement. Empirical evidences are drawn through analyzing individual borrower level credit history data obtained from two major Swedish banks between the period 1994-2000. The results show that the defaults are correlated both within and between industries but not over time (quarters). A discussion has also been presented as to how a GLMM for defaults correlation can be explained.

  • 6.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Likelihood prediction for generalized linear mixed models under covariate uncertainty2014Ingår i: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 43, nr 2, s. 219-234Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the techniques of likelihood prediction for the generalized linear mixed models. Methods of likelihood prediction is explained through a series of examples; from a classical one to more complicated ones. The examples show, in simple cases, that the likelihood prediction (LP) coincides with already known best frequentist practice such as the best linear unbiased predictor. The paper outlines a way to deal with the covariate uncertainty while producing predictive inference. Using a Poisson error-in-variable generalized linear model, it has been shown that in complicated cases LP produces better results than already know methods.

  • 7.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Computionally feasible estimation of the covariance structure in generalized linear mixed models2008Ingår i: Journal of Statistical Computation and Simulation, ISSN 0094-9655, E-ISSN 1563-5163, Vol. 78, nr 12, s. 1229-1239Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we discuss how a regression model, with a non-continuous response variable, which allows for dependency between observations, should be estimated when observations are clustered and measurements on the subjects are repeated. The cluster sizes are assumed to be large. We find that the conventional estimation technique suggested by the literature on generalized linear mixed models (GLMM) is slow and sometimes fails due to non-convergence and lack of memory on standard PCs. We suggest to estimate the random effects as fixed effects by generalized linear model and to derive the covariance matrix from these estimates. A simulation study shows that our proposal is feasible in terms of mean-square error and computation time. We recommend that our proposal be implemented in the software of GLMM techniques so that the estimation procedure can switch between the conventional technique and our proposal, depending on the size of the clusters.

  • 8.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Chen, Rui
    Liang, Yuli
    How to determine the progression of young skiers?2008Ingår i: CHANCE: New Directions for Statistics and Computing, ISSN 0933-2480, Vol. 21, nr 4, s. 13-19Artikel i tidskrift (Refereegranskat)
  • 9.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Linde, Olof
    Sweco Eurofutures.
    Nääs, Ola
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Sandén, Peter
    Sweco Eurofutures.
    Wing, Stefan
    Sweco Eurofutures.
    Utvärdering av det arbetsmarknadspolitiska projektet "Volvo Cars och dess underleverantörer"2012Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Denna rapport är en utvärdering av det arbetsmarknadspolitiska projektet "Volvo Cars och dess underleverantörer", som har genomförts av Arbetsförmedlingen i samarbete med Skolverket och Svenska ESF-rådet. Den 5 juni 2009 ansökte Sveriges regering om medel hos den Europeiska globaliseringsfonen (EGF)2 för att kunna erbjuda åtgärder för personer som blivit uppsagda från Volvo Cars AB och dess underleverantörer. Syftet med projektet var att kunna erbjuda de som blivit uppsagda kompetensutveckling, nya yrkeskunskaper och möjlighet att etablera egna företag.

    På operativ nivå drevs projektet i samverkan mellan Arbetsförmedlingen och den kom-munala yrkesvuxenutbildningen ("Yrkesvux"). Yrkesvux i Göteborgs kommun fick i upp-drag av Skolverket att samordna den del av verksamheten som berörde kommunal yr-kesvuxenutbildning. Projektet startade 1 januari 2010 och avslutades 31 maj 2011. Enligt kommissionens beslut fick medel även användas retroaktivt för insatser som hade givits till de uppsagda i form av olika arbetsmarknadsutbildningar, det s.k. snabbspåret, under 2009 innan projektet hade startat.

    Av nästan 5 000 individer i målgruppen som registrerade sig vid Arbetsförmedlingen del-tog knappt en fjärdedel i projektets insatser (exkl. vägledning). Av dessa gick 55 procent i aktiviteter enbart genom Arbetsförmedlingen, 37 procent enbart genom Yrkesvux och åtta procent genom både Arbetsförmedlingen och Yrkesvux. De vanligaste förekommande utbildningsinriktningarna var industri och bygg, fordonsindustri, transport och magasine-ring, omvårdnad och handel.

  • 10.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Nääs, Ola
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Har kommunala sommarjobb under gymnasieåren en positiv effekt på arbetskarriären senare i livet?2013Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Att erbjuda sommarjobb till ungdomar ses i många länder som ett sätt att förbättra ungdomars möjligheter att komma in och etablera sig på arbetsmarknaden. I Sverige erbjuder de flesta kommuner, delvis finansierat med statliga medel, sommarjobb till ungdomar. Den forskning som finns kring effekten av sommarjobb för ungdomar pekar dock i olika riktningar och lider ofta av metodproblem. Vi undersöker här med bättre metodologiska förutsättningar om kommunala sommarjobb för gymnasieungdomar i Falu kommun har någon positiv effekt på den postgymnasiala inkomstutvecklingen. Vi följer 2 650 ungdomar som, under första året i gymnasiet, ansökte om kommunalt sommarjobb. Vi följer dem tills de når en ålder av som mest 29 år. De kommunala sommarjobben fördelades genom ett lotteriförfarande där alla som ansökte hade lika stor chans att bli tilldelad ett sommarjobb. Vi finner ingen programeffekt för män. För kvinnor upptäcker vi en positiv effekt och då speciellt för kvinnor med låga betyg från grundskolan.

  • 11.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Nääs, Ola
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    High-School Students´ Summer Jobs and their Ensuing Labor Market Achievement: the Long Term Effect2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In part because of high and persistent youth unemployment, adolescent students’ transition from school to work is an important policy and research topic. Many countries have implemented public programs offering summer jobs or work while in high-school as measures to smooth the transition. While the immediate effect of the programs on school attendance, school grades, and disposable income is well documented, their effect on the transition to the labor market remains an open question. Observational studies have shown strong positive effects of summer jobs, but also that the estimated effect is highly vulnerable to selection bias. In this paper, some 3700 high-school students applying for summer jobs in the period 1995-2003,via a program, are followed to 30 years of age. A quarter of the applicants were randomly offered a summer job each year. Among the remaining students, 50% had a (non-program related) summer job while in high-school. We find the income, post high-school, for the offered and non-offered groups to be similar and conclude that the effect of summer jobs on the transition to the labor market is inconsequential.

  • 12.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Nääs, Ola
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Sommarjobb, arbetslivserfarenhet och framtida arbetsinkomst2015Ingår i: Arbetsmarknad & Arbetsliv, ISSN 1400-9692, Vol. 21, nr 4, s. 26-40Artikel i tidskrift (Refereegranskat)
    Abstract [sv]

    De flesta kommuner erbjuder sommarjobb till gymnasieungdomar. Vi har undersökt om denna arbetslivserfarenhet påverkar flickors framtida arbetsinkomster. Vi följde 1 447 flickor i fem till tolv år efter avslutat gymnasium. Flickorna hade under sitt första gymnasieår ansökt och slumpmässigt tilldelats sommarjobb av Falu kommun. Effekten av sommarjobbserfarenheten var positiv och betydande för dem.

  • 13.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Nääs, Ola
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    The effect of summer jobs on post-schooling incomes2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In part because of high youth unemployment, students’ transition from school to work is an important policy and research topic. Public programs offering summer jobs or work while in high school as measures to smooth the transition is commonplace. The immediate effect of the programs on school attendance, school grades, and disposable income is well documented. However, their effect on the transition to the labor market remains unsettled, partly because of a potential selection bias in previous observational studies. In this paper, 2650 first graders of high school in Falun Council, Sweden, randomly allotted summer jobs via a program in the years of 1997-2003, are followed ten years after graduation. The program led to a substantially larger accumulation of work experience while in high school for offered (particularly weak academically performing) females, but not for offered males. Hence, the immediate program effect was heterogeneous. Females were used to estimate the causal effect of work experience while in high school on post-schooling incomes. The (statistically) significant estimate implies an elasticity of 0.4. Work experience while in high school seems to be of future benefit, but the elasticity is potentially inflated due to heterogeneous effects that we were unable to account for.

  • 14.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Nääs, Ola
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    The program and treatment effect of summer jobs on girls’ post-schooling incomes2014Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Public programs (of disputed effect) offering summer jobs or work while in high school to smooth the transition from school to work is commonplace. In this paper, 1447 girls in their first grade of high school between 1997-2003 and randomly allotted summer jobs via a program in Falun (Sweden) are followed 5-12 years after graduation. The program led to a substantially larger accumulation of income while in high school. The causal effect of the high school income on post-schooling incomes was substantial and statistically significant. The implied elasticity of 0.4 is however potentially inflated dueto heterogeneous effects.

  • 15.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Nääs, Ola
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    The program and treatment effect of summer jobs on girls’ post-schooling incomes2015Ingår i: Evaluation review, ISSN 0193-841X, E-ISSN 1552-3926, Vol. 39, nr 3, s. 339-359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Public programs offering summer jobs to smooth the transition from school to work is commonplace. However, the empirical support for summer jobs is limited. This article exploits the availability of registered individual information and random allocation to summer jobs to provide empirical evidence on this issue. 

    Objectives: To identify the effect of summer job programs on the post-schooling incomes of the intended participants. Also to identify the effect of sophomore girls' high school work experience on their post-schooling incomes. 

    Research design: In this article, 1,447 sophomore girls from 1997 to 2003 are followed 5-12 years after graduation. They all applied to Falun municipality's (Sweden) summer job program, and about 25% of them were randomly allotted a job. The random allocation to a summer job is used to identify the causal effect of sophomore girls' high school income on their post-schooling incomes. 

    Subjects: All the 1,447 sophomore girls who applied to Falun municipality's summer job program during 1997-2003. 

    Measures: Annual post-schooling income is used as an outcome measure. The work experience of girls in high school is also measured in terms of total income while in high school. 

    Results: The program led to a substantially larger accumulation of income during high school as well as 19% higher post-schooling incomes. The high school income led to a post-schooling income elasticity of 0.37 which is, however, potentially heterogeneous with regard to academic ability. 

    Conclusions: Both the program effect and the causal effect of high school income on post-schooling incomes were substantial and statistically significant.

  • 16.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Hao, Chengcheng
    Carling, Kenneth
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Review of the literature on credit risk modeling: development of the past 10 years2010Ingår i: Banks and Bank Systems, ISSN 1816-7403, Vol. 5, nr 3, s. 43-60Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper traces the developments of credit risk modeling in the past 10 years. Our work can be divided into two parts: selecting articles and summarizing results. On the one hand, by constructing an ordered logit model on historical Journal of Economic Literature (JEL) codes of articles about credit risk modeling, we sort out articles which are the most related to our topic. The result indicates that the JEL codes have become the standard to classify researches in credit risk modeling. On the other hand, comparing with the classical review Altman and Saunders(1998), we observe some important changes of research methods of credit risk. The main finding is that current focuses on credit risk modeling have moved from static individual-level models to dynamic portfolio models.

  • 17.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Maengseok, Noh
    Department of Statistics, Pukyong National University, South Korea.
    Lee, Youngjo
    Department of Statistics, Seoul National University, South Korea.
    Likelihood estimate of treatment effects under selection bias2013Ingår i: Statistics and its Interface, ISSN 1938-7989, E-ISSN 1938-7997, Vol. 6, nr 3, s. 349-359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider methods for estimating the causal effects of treatment in the situation where the individuals in the treatment and the control group are self selected, i.e., the selection mechanism is not randomized. In this case, a simple comparison of treated and control outcomes will not generally yield valid estimates of casual effect. The propensity score method is frequently used for the evaluation of treatment effect. However, this method is based on some strong assumptions, which are not directly testable. In this paper, we present an alternative modelling approach to draw causal inferences by using a shared random-effect model and the computational algorithm to draw likelihood based inference with such a model. With small numerical studies and a real data analysis, we show that our approach gives not only more efficient estimates but also is less sensitive to model misspecifications, which we consider, than existing methods.

  • 18.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Noh, Maengseok
    Department of Statistics, Pukyong National Univeristy.
    Lee, Youngjo
    Department of Statistics, Seoul National Univeristy.
    Likelihood estimate of treatment effects under selection bias2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We consider methods for estimating causal effects of treatment in the situation where the individuals in the treatment and the control group are self selected, i.e., the selection mechanism is not randomized. In this case, simple comparison of treated and control outcomes will not generally yield valid estimates of casual effects. The propensity score method is frequently used for the evaluation of treatment effect. However, this method is based onsome strong assumptions, which are not directly testable. In this paper, we present an alternative modeling approachto draw causal inference by using share random-effect model and the computational algorithm to draw likelihood based inference with such a model. With small numerical studies and a real data analysis, we show that our approach gives not only more efficient estimates but it is also less sensitive to model misspecifications, which we consider, than the existing methods.

  • 19.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Rönnegård, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Shen, Xia
    Karolinska Institutet.
    Fitting conditional and simultaneous autoregressive spatial models in hglm2015Ingår i: The R Journal, ISSN 2073-4859, Vol. 7, nr 2, s. 5-18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a new version (> 2.0) of the hglm package for fitting hierarchical generalized linear models (HGLMs) with spatially correlated random effects. CAR() and SAR() families for conditional and simultaneous autoregressive random effects were implemented. Eigen decomposition of the matrix describing the spatial structure (e.g., the neighborhood matrix) was used to transform the CAR/SAR random effects into an independent, but eteroscedastic, Gaussian random effect. A linear predictor is fitted for the random effect variance to estimate the parameters in the CAR and SAR models. This gives a computationally efficient algorithm for moderately sized problems.

  • 20.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Rönnegård, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Shen, Xia
    Swedish University of Agricultural Sciences, Uppsala.
    Fitting spatial models in the R package: hglm2014Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We present a new version of the hglm package for fittinghierarchical generalized linear models (HGLM) with spatially correlated random effects. A CAR family for conditional autoregressive random effects was implemented. Eigen decomposition of the matrix describing the spatial structure (e.g. the neighborhood matrix) was used to transform the CAR random effectsinto an independent, but heteroscedastic, gaussian random effect. A linear predictor is fitted for the random effect variance to estimate the parameters in the CAR model.This gives a computationally efficient algorithm for moderately sized problems (e.g. n<5000).

  • 21.
    Alam, Moudud
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Wang, Yu
    When are non-experimental estimates close to experimental estimates?: Evidence from a study of summer job effects in Sweden2007Rapport (Övrigt vetenskapligt)
  • 22.
    Karim, Hawzheen
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Vägteknik.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Magnusson, Rolf
    Högskolan Dalarna, Akademin Industri och samhälle, Vägteknik.
    Road barrier repair costs and influencing factors2011Ingår i: Journal of transportation engineering, ISSN 0733-947X, E-ISSN 1943-5436, Vol. 137, nr 5, s. 349-359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a study that examines repair costs for different road barrier types and factors that influence these costs. The analyses focused on w-beam and cable barriers used as median barriers. To some extent, pipe barriers, Kohlswa-beam barriers, and concrete barriers were also studied. The influencing factors included in this study were road type, speed limit, barrier type, and seasonal effects. A case study was conducted in four regions of the Swedish Road Administration. Data were collected from 1,625 barrier repairs carried out during 2005 and 2006. The results show that the number of barrier repairs and the average repair cost per vehicle kilometer are higher along collision-free roads than along motorways and 4-lane roads. The results also show that the number of barrier repairs and the average repair cost per vehicle kilometer are higher for cable barrier than for other barrier types. No conclusion can be drawn regarding influence of speed limits on barrier repairs and associated costs as the result from the regions are divergent and not statistically significant. DOI: 10.1061/(ASCE)TE.1943-5436.0000227. (C) 2011 American Society of Civil Engineers.

  • 23. Lee, Youngjo
    et al.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Noh, M
    Rönnegård, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Skarin, Anna
    Analyzing spatially correlated counts with excessive zeros: a case of modeling the changes of reindeer distribution2013Rapport (Övrigt vetenskapligt)
  • 24.
    Rönnegård, Lars
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Shen, Xia
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Hglm: A package for fitting hierarchical generalized linear models2010Ingår i: The R Journal, ISSN 2073-4859, E-ISSN 2073-4859, Vol. 2, nr 2, s. 20-28Artikel i tidskrift (Refereegranskat)
    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.

  • 25.
    Saqlain, Murshid
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Mikrodataanalys.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Brandt, Daniel
    Högskolan Dalarna, Akademin Industri och samhälle, Kulturgeografi.
    Rönnegård, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Westin, Jerker
    Högskolan Dalarna, Akademin Industri och samhälle, Datateknik.
    Stochastic differential equations modelling of levodopa concentration in patients with Parkinson's disease2018Konferensbidrag (Övrigt vetenskapligt)
    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.

  • 26.
    Shen, Xia
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Fikse, Freddy
    Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala.
    Rönnegård, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    A novel generalized ridge regression method for quantitative genetics2013Ingår i: Genetics, ISSN 0016-6731, E-ISSN 1943-2631, Vol. 193, nr 4, s. 1255-1268Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As the molecular marker density grows, there is a strong need in both genome-wide association studies and genomic selection to fit models with a large number of parameters. Here we present a computationally efficient generalized ridge regression (RR) algorithmfor situations where the number of parameters largely exceeds the number of observations. The computationally demanding parts of the method depend mainly on the number ofobservations and not the number of parameters. The algorithm was implemented in the R package bigRR based on the previously developed package hglm. Using such an approach, a heteroscedastic effects model (HEM) was also developed, implemented and tested. Theefficiency for different data sizes were evaluated via simulation. The method was tested for a bacteria-hypersensitive trait in a publicly available Arabidopsis dataset including 84 inbred lines and 216 130 SNPs. The computation of all the SNP effects required less than10 seconds using a single 2.7 GHz core. The advantage in run-time makes permutationtest feasible for such a whole-genome model, so that a genome-wide significance threshold can be obtained. HEM was found to be more robust than ordinary RR (a.k.a. SNPBLUP) in terms of QTL mapping, because SNP specific shrinkage was applied instead of acommon shrinkage. The proposed algorithm was also assessed for genomic evaluation and was shown to give better predictions than ordinary RR.

  • 27. Skarin, A.
    et al.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Reindeer habitat use in relation to two small wind farms, during preconstruction, construction, and operation2017Ingår i: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 7, nr 11, s. 3870-3882Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Worldwide there is a rush toward wind power development and its associated infrastructure. In Fennoscandia, large-scale wind farms comprising several hundred windmills are currently built in important grazing ranges used for Sámi reindeer husbandry. In this study, reindeer habitat use was assessed using reindeer fecal pellet group counts in relation to two relatively small wind farms, with 8 and 10 turbines, respectively. In 2009, 1,315 15-m2 plots were established and pellet groups were counted and cleaned from the plots. This was repeated once a year in May, during preconstruction, construction, and operation of the wind farms, covering 6 years (2009-2014) of reindeer habitat use in the area. We modeled the presence/absence of any pellets in a plot at both the local (wind farm site) and regional (reindeer calving to autumn range) scale with a hierarchical logistic regression, where spatial correlation was accounted for via random effects, using vegetation type, and the interaction between distance to wind turbine and time period as predictor variables. Our results revealed an absolute reduction in pellet groups by 66% and 86% around each wind farm, respectively, at local scale and by 61% at regional scale during the operation phase compared to the preconstruction phase. At the regional, scale habitat use declined close to the turbines in the same comparison. However, at the local scale, we observed increased habitat use close to the wind turbines at one of the wind farms during the operation phase. This may be explained by continued use of an important migration route close to the wind farm. The reduced use at the regional scale nevertheless suggests that there may be an overall avoidance of both wind farms during operation, but further studies of reindeer movement and behavior are needed to gain a better understanding of the mechanisms behind this suggested avoidance.

  • 28.
    Skarin, Anna
    et al.
    SLU.
    Sandström, Per
    SLU.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Out of sight of wind turbines — Reindeer response to wind farms in operation2018Ingår i: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 8, s. 9906-9919Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To meet the expanding land use required for wind energy development, a better understanding of the effects on terrestrial animals’ responses to such development is required. Using GPS-data from 50 freely ranging female reindeer (Rangifer tarandus) in the Malå reindeer herding community, Sweden, we determined reindeer calving sites and estimated reindeer habitat selection using resource selection functions (RSF). RSFs were estimated at both second- (selection of home range) and third-order (selection within home range) scale in relation to environmental variables, wind farm (WF) development phase (before construction, construction, and operation), distance to the WFs and at the second-order scale whether the wind turbines were in or out of sight of the reindeer. We found that the distance between reindeer calving site and WFs increased during the operation phase, compared to before construction. At both scales of selection, we found a significant decrease in habitat selection of areas in proximity of the WFs, in the same comparison. The results also revealed a shift in home range selection away from habitats where wind turbines became visible toward habitats where the wind turbines were obscured by topography (increase in use by 79% at 5 km). We interpret the reindeer shift in home range selection as an effect of the wind turbines per se. Using topography and land cover information together with the positions of wind turbines could therefore help identify sensitive habitats for reindeer and improve the planning and placement of WFs. In addition, we found that operation phase of these WFs had a stronger adverse impact on reindeer habitat selection than the construction phase. Thus, the continuous running of the wind turbines making a sound both day and night seemed to have disturbed the reindeer more than the sudden sounds and increased human activity during construction work.

  • 29.
    Skarin, Anna
    et al.
    Sveriges lantbruksuniversitet.
    Sandström, Per
    Sveriges lantbruksuniversitet.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Buhot, Yann
    Sveriges lantbruksuniversitet.
    Nellemann, Christian
    Rhipto-Norwegian Center for Global Analyses.
    Renar och vindkraft II: Vindkraft i drift och effekter på renar och renskötsel2016Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Utbyggnaden av vindkraft inom renskötselområdet har ökat markant det senaste decenniet, trots att kunskapen om påverkan av vindkraftsetableringar ännu inte är fullt utredd och dokumenterad. I den här rapporten beskriver vi framförallt hur vindkraftparker i driftsfas påverkar renarna och renskötseln i tre olika områden. I Malå sameby har vi studerat kalvningsområdet kring Storliden och Jokkmokkslidens vindkraftparker. I Vilhelmina Norra sameby har vi studerat vinterbetesområdet kring Stor-Rotlidens vindkraftpark, samt Lögdeålandets betesområde med Gabrielsbergets vindkraftpark som används av Byrkije reinbetesdistrikt från Norge.

    För att få en helhetsbild av hur renarna använder sitt betesområde är det viktigt att studera renarnas betes- och förflyttningsmönster långsiktigt och över hela deras betesområde och inte bara inom det lokala området nära parken. Det är också viktigt att ta hänsyn till att renarnas betesutnyttjande skiftar från år till år och mellan olika årstider beroende på väderlek och andra yttre förutsättningar. Vi vill också understryka vikten av att kombinera den traditionella kunskapen från renskötarna med vedertagna vetenskapliga analysmetoder för att besvara de frågor som är viktiga för att kunna bedriva en hållbar renskötsel.

    Vi har undersökt renarnas användning av områdena genom att utföra spillningsinventeringar under åren 2009-2015 (endast i Malå sameby), och genom att följa renar utrustade med GPS-halsband under åren 2005-2015. Datat är insamlat före och under byggfas och under driftsfas (för Gabrielsberget finns GPS-data endast för driftsfasen). Vi har analyserat data genom att utveckla statistiska modeller för val av betesområde för varje område där vi har beräknat hur renarna förhåller sig till vindkraftparksområdet före, under och efter byggnation, och på Gabrielsberget när parken varit avstängd under 40 dagar och under drift vid olika renskötselsituationer. Genom intervjuer, möten och samtal, samt information från Gabrielsbergets vindkraftparks kontrollprogram, har vi tagit del av renskötarnas erfarenheter av hur renarnas beteende, och därmed även renskötseln, påverkats av vindkraftsutbyggnaden i respektive område.

    Våra resultat visar att renarna både på kalvnings- och på vinterbetesområden påverkas negativt av vindkraftsetableringarna (Tabell a). Renarna undviker att beta i områden där de kan se och/eller höra vindkraftsverken och föredrar att vistas i områden där vindkraftverken är skymda. I kalvningsområdet i Malå ökade användningen av skymda områden med 60 % under driftsfas. I vinterbetesområdet på Gabrielsberget, när renarna utfodrades i parken och kantbevakades intensivt för att stanna i parkområdet under driftsfas, ökade användningen av skymda områden med 13 % jämfört med när de inte var utfodrade och fick ströva mer fritt. Resultaten visar också att renarna minskar sin användning av området nära vindkraftparkerna. I kalvningslandet i Malå minskar renarna sin användning av områden inom 5 km från parkerna med 16-20 %. Vintertid vid Gabrielsbergets vindkraftpark undvek renarna parken med 3 km. Våra resultat visar även att renarnas betesro minskar inom en radie på 4 km från vindkraftparkerna under kalvningsperioden och tiden därefter i jämförelse med perioden före byggfas.

    Exakta avstånd som renarna påverkas beror på förutsättningarna i respektive område, exempelvis hur topografin ser ut eller om området är begränsat av stängsel eller annan infrastruktur. Förändringarna i habitatutnyttjande i våra studieområden blev tydligare när parkerna var centralt belägna i renarnas betesområde, som i kalvningsområdet i Malå eller i vinterbeteslandet på Gabrielsberget, medan det inte var lika tydliga effekter kring Stor-Rotlidens park, som ligger i utkanten av ett huvudbetesområde.

    Oftast är snöförhållandena bättre ur betessynpunkt högre upp i terrängen än nere i dalgångarna, på grund av stabilare temperatur, vind som blåser bort snötäcket och mer variation i topografin. Därför kan etablering av vindkraftparker i höglänta områden försämra möjligheten att använda sådana viktiga reservbetesområden under vintrar med i övrigt dåliga snöförhållanden, vilka blir allt vanligare i och med klimatförändringarna. Våra resultat tyder inte direkt på att renarna påverkats negativt under dåliga betesvintrar men fler år av studier behövs för att ytterligare klargöra hur vindkraft påverkar renarna under dessa vintrar.

    Våra studier har visat att etablering av vindkraft har konsekvenser för renskötseln under både barmarkssäsongen och under vintern, men effekterna förmodas få störst inverkan inom vinterbetesområdet där det är svårt att hitta alternativa betesområden för renarna. Under sommaren är betestillgången oftast mindre begränsad och renarna kan lättare hitta alternativa områden. En direkt konsekvens av Gabrielsbergets vindkraftpark som är placerad mitt i ett vinterbetesområde har blivit att renarna behöver tillskottsutfodras och bevakas intensivare för att de inte ska gå ut ur området. När den naturliga vandringen mellan olika betesområden störs för att renarna undviker att vistas i ett område kan det leda till att den totala tillgången till naturligt bete minskar och att man permanent måste tillskottsutfodra, alternativt minska antalet renar.

    Annan infrastruktur som vägar och kraftledningar påverkar också renarna. Vid Storliden och Jokkmokksliden och vid Stor-Rotliden där data samlats in innan vindkraftparken uppfördes visar våra resultat att renarna undviker de omkringliggande landsvägarna redan innan parkerna etablerades. Vid Stor-Rotliden ökar dock renarna användningen av områden nära vägarna efter att parken är byggd. På Gabrielsberget, där vi endast har data under drifttiden, är renarna närmare vägarna (även stora vägar som E4) när renskötarna minskar på kantbevakningen för att inte hålla renarna nära parken. Detta ökar naturligtvis risken för trafikolyckor och innebär att renskötarna måste bevaka dessa områden intensivare.

    Sist i rapporten presenterar vi förslag till åtgärder som kan användas för att underlätta arbetet för renskötseln om det är så att en vindkraftpark redan är byggd. Några exempel på åtgärder som är direkt kopplat till parken är att stänga av vägarna in i vindkraftparken för att förhindra nöjeskörning med skoter och bil under den tiden renarna vistas i området samt tät dialog mellan vindkraftsbolag och sameby angående vinterväghållningen av vägarna till och inom vindkraftparken. Andra mer regionala åtgärder för att förbättra förutsättningarna för renskötselarbetet på andra platser för samebyn, kan vara att sätta stängsel längst större vägar och järnvägar (t.ex. E4:an eller stambanan) i kombination med strategiskt utplacerade ekodukter. Detta för att underlätta och återställa möjligheterna till renarnas fria strövning och renskötarnas flytt av renar mellan olika betesområden.   

  • 30.
    Svenson, Kristin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Mikrodataanalys.
    McRobbie, S.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Detecting road pavement deterioration with finite mixture models2019Ingår i: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 20, nr 4, s. 458-465Artikel i tidskrift (Refereegranskat)
    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.

  • 31.
    Thomas, Ilias
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Mikrodataanalys.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Bergquist, Filip
    Johansson, Dongni
    Memedi, Mevludin
    Nyholm, Dag
    Westin, Jerker
    Högskolan Dalarna, Akademin Industri och samhälle, Datateknik.
    Sensor-based algorithmic dosing suggestions for oral administration of levodopa/carbidopa microtablets for Parkinson's disease: a first experience2019Ingår i: Journal of Neurology, ISSN 0340-5354, E-ISSN 1432-1459, Vol. 266, nr 3, s. 651-658Artikel i tidskrift (Refereegranskat)
    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.

  • 32.
    Thomas, Ilias
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Bergquist, Filip
    Senek, Marina
    Nyholm, Dag
    Westin, Jerker
    Högskolan Dalarna, Akademin Industri och samhälle, Datateknik.
    Individual levodopa dosing suggestions based on a single dose test2016Konferensbidrag (Övrigt vetenskapligt)
  • 33.
    Thomas, Ilias
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Mikrodataanalys.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Nyholm, Dag
    Senek, Marina
    Westin, Jerker
    Högskolan Dalarna, Akademin Industri och samhälle, Datateknik.
    Individual dose-response models for levodopa infusion dose optimization2018Ingår i: International Journal of Medical Informatics, ISSN 1386-5056, E-ISSN 1872-8243, Vol. 112, s. 137-142Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background and Objective

    To achieve optimal effect with continuous infusion treatment in Parkinson’s disease (PD), the individual doses (morning dose and continuous infusion rate) are titrated by trained medical personnel. This study describes an algorithmic method to derive optimized dosing suggestions for infusion treatment of PD, by fitting individual dose-response models. The feasibility of the proposed method was investigated using patient chart data.

    Methods

    Patient records were collected at Uppsala University hospital which provided dosing information and dose-response evaluations. Mathematical optimization was used to fit individual patient models using the records’ information, by minimizing an objective function. The individual models were passed to a dose optimization algorithm, which derived an optimized dosing suggestion for each patient model.

    Results

    Using data from a single day’s admission the algorithm showed great ability to fit appropriate individual patient models and derive optimized doses. The infusion rate dosing suggestions had 0.88 correlation and 10% absolute mean relative error compared to the optimal doses as determined by the hospital’s treating team. The morning dose suggestions were consistency lower that the optimal morning doses, which could be attributed to different dosing strategies and/or lack of on-off evaluations in the morning.

    Conclusion

    The proposed method showed promise and could be applied in clinical practice, to provide the hospital personnel with additional information when making dose adjustment decisions.

  • 34.
    Thomas, Ilias
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Senek, Marina
    Uppsala University Hospital.
    Dag, Nyholm
    Uppsala University Hospital.
    Westin, Jerker
    Högskolan Dalarna, Akademin Industri och samhälle, Datateknik.
    Minimizing levodopa titration period for Parkinson’s disease2016Konferensbidrag (Övrigt vetenskapligt)
  • 35.
    Thomas, Ilias
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Mikrodataanalys.
    Westin, Jerker
    Högskolan Dalarna, Akademin Industri och samhälle, Datateknik.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Bergquist, F.
    Nyholm, D.
    Senek, M.
    Memedi, Mevludin
    Högskolan Dalarna, Akademin Industri och samhälle, Datateknik.
    A treatment–response index from wearable sensors for quantifying Parkinson's disease motor states2018Ingår i: IEEE journal of biomedical and health informatics, ISSN 2168-2194, E-ISSN 2168-2208, Vol. 22, nr 5, s. 1341-1349Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The goal of this study was to develop an algorithm that automatically quantifies motor states (off,on,dyskinesia) in Parkinson's disease (PD), based on accelerometry during a hand pronation-supination test. Clinician's ratings using the Treatment Response Scale (TRS), ranging from -3 (very Off) to 0 (On) to +3 (very dyskinetic), was used as target. For that purpose, 19 participants with advanced PD and 22 healthy persons were recruited in a single center open label clinical trial in Uppsala, Sweden. The trial consisted of single levodopa dose experiments for the people with PD (PwP), where participants were asked to perform standardized wrist rotation tests, using each hand, before and at pre-specified time points after the dose. The participants used wrist sensors containing a 3D accelerometer and gyroscope. Features to quantify the level, variation and asymmetry of the sensor signals, three-level Discrete Wavelet Transform features and approximate entropy measures were extracted from the sensors data. At the time of the tests, the PwP were video recorded. Three movement disorder specialists rated the participants’ state on the TRS scale. A Treatment Response Index from Sensors (TRIS) was constructed to quantify the motor states based on the wrist rotation tests. Different machine learning algorithms were evaluated to map the features derived from the sensor data to the ratings provided by the three specialists. Results from cross validation, both in 10-fold and a leave-one-individual out setting, showed good predictive power of a support vector machine model and high correlation to the TRS scale. Values at the end tails of the TRS scale were under and over predicted due to the lack of observations at those values but the model managed to accurately capture the dose - effect profiles of the patients. In addition, the TRIS had good test-retest reliability on the baseline levels of the PD participants (Intraclass correlation coefficient of 0.83) and reasonable sensitivity to levodopa treatment (0.33 for the TRIS). For a series of test occasions the proposed algorithms provided dose - effect time profiles for participants with PD, which could be useful during therapy individualization of people suffering from advanced PD

  • 36.
    Youngjo, Lee
    et al.
    Seoul National University.
    Alam, Moudud
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Noh, Maengseok
    Pukyong National University, Korea.
    Rönnegård, Lars
    Högskolan Dalarna, Akademin Industri och samhälle, Statistik.
    Skarin, Anna
    Swedish University of Agricultural Science, Uppsala.
    Spatial modeling of data with excessive zeros applied to reindeer pellet-group counts2016Ingår i: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 6, nr 19, s. 7047-7056Artikel i tidskrift (Refereegranskat)
    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.

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