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  • 1. Ahman, Birgitta
    et al.
    Svensson, Kristin
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    High female mortality resulting in herd collapse in free-ranging domesticated reindeer (Rangifer tarandus tarandus) in Sweden2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 10, e111509Article in journal (Refereed)
    Abstract [en]

    Reindeer herding in Sweden is a form of pastoralism practised by the indigenous Sami population. The economy is mainly based on meat production. Herd size is generally regulated by harvest in order not to overuse grazing ranges and keep a productive herd. Nonetheless, herd growth and room for harvest is currently small in many areas. Negative herd growth and low harvest rate were observed in one of two herds in a reindeer herding community in Central Sweden. The herds (A and B) used the same ranges from April until the autumn gathering in October-December, but were separated on different ranges over winter. Analyses of capture-recapture for 723 adult female reindeer over five years (2007-2012) revealed high annual losses (7.1% and 18.4%, for herd A and B respectively). A continuing decline in the total reindeer number in herd B demonstrated an inability to maintain the herd size in spite of a very small harvest. An estimated breakpoint for when herd size cannot be kept stable confirmed that the observed female mortality rate in herd B represented a state of herd collapse. Lower calving success in herd B compared to A indicated differences in winter foraging conditions. However, we found only minor differences in animal body condition between the herds in autumn. We found no evidence that a lower autumn body mass generally increased the risk for a female of dying from one autumn to the next. We conclude that the prime driver of the on-going collapse of herd B is not high animal density or poor body condition. Accidents or disease seem unlikely as major causes of mortality. Predation, primarily by lynx and wolverine, appears to be the most plausible reason for the high female mortality and state of collapse in the studied reindeer herding community.

  • 2.
    AIDOO, ERIC
    Dalarna University, School of Technology and Business Studies, Statistics.
    MODELLING AND FORECASTING INFLATION RATES IN GHANA: AN APPLICATION OF SARIMA MODELS2010Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Ghana faces a macroeconomic problem of inflation for a long period of time. The problem in somehow slows the economic growth in this country. As we all know, inflation is one of the major economic challenges facing most countries in the world especially those in African including Ghana. Therefore, forecasting inflation rates in Ghana becomes very important for its government to design economic strategies or effective monetary policies to combat any unexpected high inflation in this country. This paper studies seasonal autoregressive integrated moving average model to forecast inflation rates in Ghana. Using monthly inflation data from July 1991 to December 2009, we find that ARIMA (1,1,1)(0,0,1)12 can represent the data behavior of inflation rate in Ghana well. Based on the selected model, we forecast seven (7) months inflation rates of Ghana outside the sample period (i.e. from January 2010 to July 2010). The observed inflation rate from January to April which was published by Ghana Statistical Service Department fall within the 95% confidence interval obtained from the designed model. The forecasted results show a decreasing pattern and a turning point of Ghana inflation in the month of July.

  • 3.
    AJMAL, KHAN
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    HAN, YANG
    Dalarna University, School of Technology and Business Studies, Statistics.
    An Analysis of the Telecommunications Business in China by Linear Regression2010Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [en]

    In this paper, we study the influence of the National Telecom Business Volume by the data in 2008 that have been published in China Statistical Yearbook of Statistics. We illustrate the procedure of modeling “National Telecom Business Volume” on the following eight variables, GDP, Consumption Levels, Retail Sales of Social Consumer Goods Total Renovation Investment, the Local Telephone Exchange Capacity, Mobile Telephone Exchange Capacity, Mobile Phone End Users, and the Local Telephone End Users. The testing of heteroscedasticity and multicollinearity for model evaluation is included. We also consider AIC and BIC criterion to select independent variables, and conclude the result of the factors which are the optimal regression model for the amount of telecommunications business and the relation between independent variables and dependent variable. Based on the final results, we propose several recommendations about how to improve telecommunication services and promote the economic development.

  • 4.
    AJMAL, KHAN
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    TAHIR MAHMOOD, HASHMI
    Dalarna University, School of Technology and Business Studies, Statistics.
    Daily Calls Volume Forecasting2010Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    A massive amount has been written about forecasting but few articles are written about the development of time series models of call volumes for emergency services. In this study, we use different techniques for forecasting and make the comparison of the techniques for the call volume of the emergency service Rescue 1122 Lahore, Pakistan. For the purpose of this study data is taken from emergency calls of Rescue 1122 from 1st January 2008 to 31 December 2009 and 731 observations are used. Our goal is to develop a simple model that could be used for forecasting the daily call volume. Two different approaches are used for forecasting the daily call volume Box and Jenkins (ARIMA) methodology and Smoothing methodology. We generate the models for forecasting of call volume and present a comparison of the two different techniques.

  • 5.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    An efficient algorithm for the pseudo likelihood estimation of the generalized linear mixed models (GLMM) with correlated random effects2009Report (Other academic)
    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.

  • 6.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    An efficient estimation of the GLMM with correlated random effects2008In: COMPSTAT'2008: International Conference on Computational Statistics / [ed] Moudud, Alam, Porto-Portugal, 2008Conference paper (Other academic)
    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.

  • 7.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Feasible computation of the generalized linear mixed models with application to credit risk modelling2010Doctoral thesis, monograph (Other academic)
    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.

  • 8.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Feasible estimation of generalized linear mixed models (GLMM) with weak dependency between groups2010Manuscript (preprint) (Other academic)
    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.

  • 9.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Industry shocks and empirical evidences on defaults comovement2009Report (Other academic)
    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.

  • 10.
    Alam, Moudud
    Dalarna University, School of Technology and Business Studies, Statistics.
    Likelihood prediction for generalized linear mixed models under covariate uncertainty2014In: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 43, no 2, 219-234 p.Article in journal (Refereed)
    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.

  • 11.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Computionally feasible estimation of the covariance structure in generalized linear mixed models2008In: Journal of Statistical Computation and Simulation, ISSN 0094-9655, E-ISSN 1563-5163, Vol. 78, no 12, 1229-1239 p.Article in journal (Refereed)
    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.

  • 12.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Chen, Rui
    Liang, Yuli
    How to determine the progression of young skiers?2008In: CHANCE: New Directions for Statistics and Computing, ISSN 0933-2480, Vol. 21, no 4, 13-19 p.Article in journal (Refereed)
  • 13.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Linde, Olof
    Sweco Eurofutures.
    Nääs, Ola
    Dalarna University, School of Technology and Business Studies, Statistics.
    Sandén, Peter
    Sweco Eurofutures.
    Wing, Stefan
    Sweco Eurofutures.
    Utvärdering av det arbetsmarknadspolitiska projektet "Volvo Cars och dess underleverantörer"2012Report (Other academic)
    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.

  • 14.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Nääs, Ola
    Dalarna University, School of Technology and Business Studies, Statistics.
    Har kommunala sommarjobb under gymnasieåren en positiv effekt på arbetskarriären senare i livet?2013Report (Other academic)
    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.

  • 15.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Nääs, Ola
    Dalarna University, School of Technology and Business Studies, Statistics.
    High-School Students´ Summer Jobs and their Ensuing Labor Market Achievement: the Long Term Effect2013Report (Other academic)
    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.

  • 16.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Nääs, Ola
    Dalarna University, School of Technology and Business Studies, Statistics.
    Sommarjobb, arbetslivserfarenhet och framtida arbetsinkomst2015In: Arbetsmarknad & Arbetsliv, ISSN 1400-9692, Vol. 21, no 4, 26-40 p.Article in journal (Refereed)
    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.

  • 17.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Nääs, Ola
    Dalarna University, School of Technology and Business Studies, Statistics.
    The effect of summer jobs on post-schooling incomes2013Report (Other academic)
    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.

  • 18.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Nääs, Ola
    Dalarna University, School of Technology and Business Studies, Statistics.
    The program and treatment effect of summer jobs on girls’ post-schooling incomes2015In: Evaluation review, ISSN 0193-841X, E-ISSN 1552-3926, Vol. 39, no 3, 339-359 p.Article in journal (Refereed)
    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.

  • 19.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Nääs, Ola
    Dalarna University, School of Technology and Business Studies, Statistics.
    The program and treatment effect of summer jobs on girls’ post-schooling incomes2014Report (Other academic)
    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.

  • 20.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Hao, Chengcheng
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Review of the literature on credit risk modeling: development of the past 10 years2010In: Banks and Bank Systems, ISSN 1816-7403, Vol. 5, no 3, 43-60 p.Article in journal (Refereed)
    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.

  • 21.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    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 bias2013In: Statistics and its Interface, ISSN 1938-7989, E-ISSN 1938-7997, Vol. 6, no 3, 349-359 p.Article in journal (Refereed)
    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.

  • 22.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Noh, Maengseok
    Department of Statistics, Pukyong National Univeristy.
    Lee, Youngjo
    Department of Statistics, Seoul National Univeristy.
    Likelihood estimate of treatment effects under selection bias2012Report (Other academic)
    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.

  • 23.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Shen, Xia
    Karolinska Institutet.
    Fitting conditional and simultaneous autoregressive spatial models in hglm2015In: The R Journal, ISSN 2073-4859, Vol. 7, no 2, 5-18 p.Article in journal (Refereed)
    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.

  • 24.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Shen, Xia
    Swedish University of Agricultural Sciences, Uppsala.
    Fitting spatial models in the R package: hglm2014Report (Other academic)
    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).

  • 25.
    Alam, Moudud
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Wang, Yu
    When are non-experimental estimates close to experimental estimates?: Evidence from a study of summer job effects in Sweden2007Report (Other academic)
  • 26. Al-Sarraj, Razaw
    et al.
    Qie, Weigang
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Evaluation of variance component estimators based on Henderson's Method2011Report (Other academic)
  • 27. Alvarez-Castro, J.M.
    et al.
    Carlborg, Ö.
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Estimation and interpretation of genetic effects with epistasis using the NOIA model2012In: Quantitative trait loci (QTL): Methods and Protocols / [ed] Scott A. Rifkin, Humana Press, 2012, 191-204 p.Chapter in book (Other academic)
    Abstract [en]

    We introduce this communication with a brief outline of the historical landmarks in genetic modeling, especially concerning epistasis. Then, we present methods for the use of genetic modeling in QTL analyses. In particular, we summarize the essential expressions of the natural and orthogonal interactions (NOIA) model of genetic effects. Our motivation for reviewing that theory here is twofold. First, this review presents a digest of the expressions for the application of the NOIA model, which are often mixed with intermediate and additional formulae in the original articles. Second, we make the required theory handy for the reader to relate the genetic concepts to the particular mathematical expressions underlying them. We illustrate those relations by providing graphical interpretations and a diagram summarizing the key features for applying genetic modeling with epistasis in comprehensive QTL analyses. Finally, we briefly review some examples of the application of NOIA to real data and the way it improves the interpretability of the results.

  • 28. Andersson, J.
    et al.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Köster, M.
    Rosén, M.
    Dödlighet efter hjärtinfarkt har minskat i nästan alla landsting under 1990-talet: Störst förbättringar i de landsting som hade sämst resultat från början2003In: Läkartidningen, ISSN 0023-7205, no 100:37, 2838-2844 p.Article in journal (Refereed)
  • 29. Bennmarker, Helge
    et al.
    Carling, Kenneth
    Dalarna University, School of Technology and Business Studies, Statistics.
    Holmlund, Bertil
    Do Benefit Hikes Damage Job Findings?: Evidence from Swedish Unemployment Insurance Reforms2007In: Labour, ISSN 1121-7081, E-ISSN 1467-9914, Vol. 21, no 1, 85-120 p.Article in journal (Refereed)
    Abstract [en]

    In 2001 and 2002, Sweden introduced several unemployment insurance reforms. A major innovation in the first reform was the introduction of a two-tiered benefit structure for some unemployed individuals. This system involved supplementary compensation during the first 20 weeks of unemployment. The 2002 reform retained the two-tiered benefit structure but involved also substantial benefit hikes for spells exceeding 20 weeks. This paper examines how these reforms affected transitions from unemployment to employment. We take advantage of the fact that the reforms had quasi-experimental features where the 'treatments' differed considerably among unemployed individuals. We find that the reforms had strikingly different effects on job finding among men and women. The two reforms in conjunction are estimated to have increased the expected duration of unemployment among men but to have decreased the duration of unemployment among women. The overall effect on the duration of unemployment is not statistically different from zero. However, the reforms reduced job finding among men who remained unemployed for more than 20 weeks.

  • 30. Bertilson, B
    et al.
    Bring, Johan
    Dalarna University, School of Technology and Business Studies, Statistics.
    Sjöblom, A
    Sundell, K
    Strender, L
    Inter-examiner reliability in the assessment of low back pain (LBP) using the Kirkaldy-Willis classification (KWC)2006In: European spine journal, ISSN 0940-6719, E-ISSN 1432-0932, Vol. 15, no 11, 1695-1703 p.Article in journal (Refereed)
    Abstract [en]

    Reliable classification systems and clinical tests are sought for the care of patients with low back pain (LBP). The objectives of this clinical study were to evaluate inter-examiner reliability in the classification of patients with LBP, the influence of radiological findings on the classification and the reliability of some clinical tests. Two examiners independently assessed 50 outpatients with LBP. Inter-examiner reliability in classification of patients with LBP using Kirkkaldy-Willis classification (KWC) system and in 30 clinical tests was calculated as percentage agreement and kappa coefficients (?). Inter-examiner reliability was excellent (?>0.8) for classification according to KWC. Radiological findings did not influence the reliability. Age of the patient, movement range, and pain and neurological signs seemed to guide the decision on classification. The reliability of clinical tests was good (?>0.6) in 6 tests and moderate (?>0.4) in 12 tests. Good inter-examiner reliability was found for the SLR test, movement range and sensibility testing with spurs in dermatome areas. We conclude that the KWC for classifying patients with LBP seems to be a reliable classification system depending on a few key observations and that moderate and good inter-examiner reliability can be achieved in several clinical tests in the assessment of LBP.

  • 31. Besnier, Francois
    et al.
    Wahlberg, Per
    Rönnegård, Lars
    Dalarna University, School of Technology and Business Studies, Statistics.
    Ek, Weronika
    Andersson, Leif
    Siegel, Paul
    Carlborg, Örjan
    Fine mapping and replication of QTL in outbred chicken advanced intercross lines2011In: Genetics Selection Evolution, ISSN 0999-193X, E-ISSN 1297-9686, Vol. 43, 3Article in journal (Refereed)
    Abstract [en]

    Background: Linkage mapping is used to identify genomic regions affecting the expression of complex traits. However, when experimental crosses such as F2 populations or backcrosses are used to map regions containing a Quantitative Trait Locus (QTL), the size of the regions identified remains quite large, i.e. 10 or more Mb. Thus, other experimental strategies are needed to refine the QTL locations. Advanced Intercross Lines (AIL) are produced by repeated intercrossing of F2 animals and successive generations, which decrease linkage disequilibrium in a controlled manner. Although this approach is seen as promising, both to replicate QTL analyses and fine-map QTL, only a few AIL datasets, all originating from inbred founders, have been reported in the literature.

    Methods: We have produced a nine-generation AIL pedigree (n = 1529) from two outbred chicken lines divergently selected for body weight at eight weeks of age. All animals were weighed at eight weeks of age and genotyped for SNP located in nine genomic regions where significant or suggestive QTL had previously been detected in the F2 population. In parallel, we have developed a novel strategy to analyse the data that uses both genotype and pedigree information of all AIL individuals to replicate the detection of and fine-map QTL affecting juvenile body weight.

    Results: Five of the nine QTL detected with the original F2 population were confirmed and fine-mapped with the AIL, while for the remaining four, only suggestive evidence of their existence was obtained. All original QTL were confirmed as a single locus, except for one, which split into two linked QTL.

    Conclusions: Our results indicate that many of the QTL, which are genome-wide significant or suggestive in the analyses of large intercross populations, are true effects that can be replicated and fine-mapped using AIL. Key factors for success are the use of large populations and powerful statistical tools. Moreover, we believe that the statistical methods we have developed to efficiently study outbred AIL populations will increase the number of organisms for which in-depth complex traits can be analyzed.

  • 32.
    Brandt, Daniel
    et al.
    Dalarna University, School of Technology and Business Studies, Human Geography.
    Heldt, Tobias
    Dalarna University, School of Technology and Business Studies, Economics.
    Wikström, Daniel
    Dalarna University, School of Technology and Business Studies, Statistics.
    Potential research areas for big data in tourism2016In: Proceedings of the IFITTtalk@Östersund Workshop on Big Data & Business Intelligence in the Travel & Tourism Domain / [ed] Fuchs, M., Lexhagen, M. & Höpken, W., 2016Conference paper (Refereed)
  • 33.
    Brandt, Daniel
    et al.
    Dalarna University, School of Technology and Business Studies, Human Geography.
    Wikström, Daniel
    Dalarna University, School of Technology and Business Studies, Statistics.
    Education and careers in the Swedish tourism sector: How important is education for building a successful career?2015Conference paper (Refereed)
  • 34.
    Bring, Johan
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Skånér, Y.
    Backlund, L.
    Montgomery, H.
    Strender, L-E
    General practitioners' reasoning when considering the diagnosis heart failure: a think-aloud study2005In: BMC Family Practice, ISSN 1471-2296, Vol. 6, no 1Article in journal (Refereed)
  • 35.
    Bring, Johan
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Skånér, Y.
    Strender, L-E
    Selecting representative case vignettes for clinical judgement studies: Examples from two heart failure studies2005In: Quality and quantity, ISSN 0033-5177, E-ISSN 1573-7845, Vol. 38, no 5, 621-635 p.Article in journal (Refereed)
  • 36.
    Bring, Johan
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Taube, Adam
    Introduktion till Medicinsk Statistik2006Book (Other academic)
  • 37.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Alam, M.M.
    Computanionally feasible estimation of the covariance structure in Generalized linear mixed models (GLMM)2007Report (Other academic)
    Abstract [en]

    In this paper we discuss how a regression model, with a non-continuous response variable, that allows for dependency between observations should be estimated when observations are clustered and there are repeated measurements on the subjects. 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 often fails due to non-convergence and lack of memory on standard PCs. We suggest to estimate the random effects as fixed effects by GLM and 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.

  • 38.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Bennmarker, H.
    Holmlund, B.
    Leder höjd a-kassa till längre arbetslöshetstider?: Enstudie av de svenska förändringarna 2001-20022005Report (Other academic)
  • 39.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Bennmarker, Helge
    Holmlund, Bertil
    Do benefit hikes damage job finding? Evidence from Swedish unemployment insurance reforms2005Report (Other academic)
    Abstract [en]

    In 2001 and 2002, Sweden introduced several unemployment insurance reforms. A major innovation in the first reform was the introduction of a two-tiered benefit structure for some unemployed individuals. This system involved supplementary compensation during the first 20 weeks of unemployment. The 2002 reform retained the two-tiered benefit structure but involved also substantial benefit hikes for spells exceeding 20 weeks. This paper examines how these reforms affected transitions from unemployment to employment. We take advantage of the fact that the reforms had quasi-experimental features where the “treatments” differed considerably among unemployed individuals. We find that the reforms had strikingly different effects on job finding among men and women. The two reforms in conjunction are estimated to have LQFUHDVHG the expected duration of unemployment among men but to have GHFUHDVHG the duration of unemployment among women. The overall effect on the duration of unemployment is not statistically different from zero. However, the reforms reduced job finding among males who remained unemployed for more than 20 weeks.

  • 40.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Forslund, Anders
    Bennmarker, Helge
    Vem blir långtidsarbetslös?2007Report (Other academic)
    Abstract [sv]

    I ett antal länder har man på senare tid utvecklat statistiska modeller som ett stöd för förmedlarna att förutsäga vilka arbetslösa som riskerar att bli långtidsarbetslösa, s k profiling. I den här rapporten redovisar vi resultaten av att skatta hasardmodeller för att förutsäga vem som riskerar att bli långtidsarbetslös bland dem som registrerar sig som arbetslösa arbetssökande vid arbetsförmedlingen. Av resultaten framgår det att den skattade modellen lyckas relativt väl med att förutsäga vem som riskerar att bli arbetslös i minst sex månader – träffsäkerheten i prognoser som görs utanför modellens skattningsperiod är nästan 70 %.

  • 41.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    GRASP and statistical bounds for heuristic solutions to combinatorial problems2016Report (Other academic)
    Abstract [en]

    The quality of a heuristic solution to a NP-hard combinatorial problem is hard to assess. A few studies have advocated and tested statistical bounds as a method for assessment. These studies indicate that statistical bounds are superior to the more widely known and used deterministic bounds. However, the previous studies have been limited to a few metaheuristics and combinatorial problems and, hence, the general performance of statistical bounds in combinatorial optimization remains an open question. This work complements the existing literature on statistical bounds by testing them on the metaheuristic Greedy Randomized Adaptive Search Procedures (GRASP) and four combinatorial problems. Our findings confirm previous results that statistical bounds are reliable for the p-median problem, while we note that they also seem reliable for the set covering problem. For the quadratic assignment problem, the statistical bounds has previously been found reliable when obtained from the Genetic algorithm whereas in this work they found less reliable. Finally, we provide statistical bounds to four 2-path network design problem instances for which the optimum is currently unknown.

  • 42.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Human Geography.
    Does Euclidean distance work well when the p-median model is applied in rural areas?2012In: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 201, no 1, 83-97 p.Article in journal (Refereed)
    Abstract [en]

    The p-median model is used to locate P centers to serve a geographically distributed population. A cornerstone of such a model is the measure of distance between a service center and demand points, i.e. the location of the population (customers, pupils, patients, and so on). Evidence supports the current practice of using Euclidean distance. However, we find that the location of multiple hospitals in a rural region of Sweden with anon-symmetrically distributed population is quite sensitive to distance measure, and somewhat sensitive to spatial aggregation of demand points.

  • 43.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Human Geography.
    Methodological issues in applying Location Models to Rural areas2010Report (Other academic)
    Abstract [en]

    Location Models are usedfor planning the location of multiple service centers in order to serve a geographicallydistributed population. A cornerstone of such models is the measure of distancebetween the service center and a set of demand points, viz, the location of thepopulation (customers, pupils, patients and so on). Theoretical as well asempirical evidence support the current practice of using the Euclidian distancein metropolitan areas. In this paper, we argue and provide empirical evidencethat such a measure is misleading once the Location Models are applied to ruralareas with heterogeneous transport networks. This paper stems from the problemof finding an optimal allocation of a pre-specified number of hospitals in alarge Swedish region with a low population density. We conclude that the Euclidianand the network distances based on a homogenous network (equal travel costs inthe whole network) give approximately the same optimums. However networkdistances calculated from a heterogeneous network (different travel costs indifferent parts of the network) give widely different optimums when the numberof hospitals increases.  In terms ofaccessibility we find that the recent closure of hospitals and the in-optimallocation of the remaining ones has increased the average travel distance by 75%for the population. Finally, aggregation the population misplaces the hospitalsby on average 10 km.

  • 44.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Information Systems. Dalarna University, School of Technology and Business Studies, Human Geography.
    Var ska sjukhusen ligga?2013In: Ekonomiska samfundets tidskrift, ISSN 0013-3183, E-ISSN 2323-1378, no 3, 165-171 p.Article in journal (Refereed)
    Abstract [sv]

    Denna artikel visar på en metod för att undersöka hur optimal befolkningens fysiska tillgänglighet till sjukvården är. Detta är relevant med tanke på den svenska storregionala omdaningen som säkerligen kommer provocera fram omprövningar av sjukhusens framtida placering.

    Med Dalarna som exempel fann vi att en ökning från dagens två till tre optimalt lokaliserade sjukhus skulle minska befolkningens genomsnittliga reseavstånd med 25 %.

    På basis av transportsektorns standardkalkyler för samhällsekonomisk effekter vid resande, samt av kostnader för drift av sjukvård sluter vi dessutom oss till att en komplettering av nuvarande två sjukhus i Dalarna med ett tredje vore samhällsekonomiskt effektivt.

  • 45.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Information Systems. Dalarna University, School of Technology and Business Studies, Human Geography.
    Meng, Xiangli
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rudholm, Niklas
    Dalarna University, School of Technology and Business Studies, Economics. HUI Research.
    Measuring CO2 emissions induced by online and brick-and-mortar retailing2014Report (Other academic)
    Abstract [en]

    We develop a method for empirically measuring the difference in carbon footprint between traditional and online retailing (“e-tailing”) from entry point to a geographical area to consumer residence. The method only requires data on the locations of brick-and-mortar stores, online delivery points, and residences of the region’s population, and on the goods transportation networks in the studied region. Such data are readily available in most countries, so the method is not country or region specific. The method has been evaluated using data from the Dalecarlia region in Sweden, and is shown to be robust to all assumptions made. In our empirical example, the results indicate that the average distance from consumer residence to a brick-and-mortar retailer is 48.54 km in the studied region, while the average distance to an online delivery point is 6.7 km. The results also indicate that e-tailing increases the average distance traveled from the regional entry point to the delivery point from 47.15 km for a brick-and-mortar store to 122.75 km for the online delivery points. However, as professional carriers transport the products in bulk to stores or online delivery points, which is more efficient than consumers’ transporting the products to their residences, the results indicate that consumers switching from traditional to e-tailing on average reduce their CO2 footprints by 84% when buying standard consumer electronics products. 

  • 46.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Information Systems. Dalarna University, School of Technology and Business Studies, Human Geography.
    Meng, Xiangli
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rudholm, Niklas
    Dalarna University, School of Technology and Business Studies, Economics. HUI Research.
    Measuring CO2 emissions induced by online and brick-and-mortar retailing2014Report (Other academic)
    Abstract [en]

    We develop a method for empirically measuring the difference in carbon footprint between traditional and online retailing (“e-tailing”) from entry point to a geographical area to consumer residence. The method only requires data on the locations of brick-and-mortar stores, online delivery points, and residences of the region’s population, and on the goods transportation networks in the studied region. Such data are readily available in most countries, so the method is not country or region specific. The method has been evaluated using data from the Dalecarlia region in Sweden, and is shown to be robust to all assumptions made. In our empirical example, the results indicate that the average distance from consumer residence to a brick-and-mortar retailer is 48.54 km in the studied region, while the average distance to an online delivery point is 6.7 km. The results also indicate that e-tailing increases the average distance traveled from the regional entry point to the delivery point from 47.15 km for a brick-and-mortar store to 122.75 km for the online delivery points. However, as professional carriers transport the products in bulk to stores or online delivery points, which is more efficient than consumers’ transporting the products to their residences, the results indicate that consumers switching from traditional to e-tailing on average reduce their CO2 footprints by 84% when buying standard consumer electronics products. 

  • 47.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Information Systems. Dalarna University, School of Technology and Business Studies, Human Geography.
    Meng, Xiangli
    Dalarna University, School of Technology and Business Studies, Statistics.
    Rudholm, Niklas
    Dalarna University, School of Technology and Business Studies, Economics.
    Measuring transport related CO2 emissions induced by online and brick-and-mortar retailing2015In: Transportation Research Part D: Transport and Environment, ISSN 1361-9209, E-ISSN 1879-2340, Vol. 40, 28-42 p.Article in journal (Refereed)
    Abstract [en]

    We develop a method for empirically measuring the difference in transport related carbon footprint between traditional and online retailing (“e-tailing”) from entry point to a geographical area to consumer residence. The method only requires data on the locations of brick-and-mortar stores, online delivery points, and residences of the region’s population, and on the goods transportation networks in the studied region. Such data are readily available in most countries. The method has been evaluated using data from the Dalecarlia region in Sweden, and is shown to be robust to all assumptions made. In our empirical example, the results indicate that the average distance from consumer residence to a brick-and-mortar retailer is 48.54 km in the studied region, while the average distance to an online delivery point is 6.7 km. The results also indicate that e-tailing increases the average distance traveled from the regional entry point to the delivery point from 47.15 km for a brick-and-mortar store to 122.75 km for the online delivery points. However, as professional carriers transport the products in bulk to stores or online delivery points, which is more efficient than consumers’ transporting the products to their residences, the results indicate that consumers switching from traditional to e-tailing on average reduce their transport CO2 footprints by 84% when buying standard consumer electronics products. 

  • 48.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Human Geography.
    Rebreyend, Pascal
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    An empirical test of the gravity p-median model2012Report (Other academic)
    Abstract [en]

    A customer is presumed to gravitate to a facility by the distance to it and the attractiveness of it. However regarding the location of the facility, the presumption is that the customer opts for the shortest route to the nearest facility.This paradox was recently solved by the introduction of the gravity p-median model. The model is yet to be implemented and tested empirically. We implemented the model in an empirical problem of locating locksmiths, vehicle inspections, and retail stores ofv ehicle spare-parts, and we compared the solutions with those of the p-median model. We found the gravity p-median model to be of limited use for the problem of locating facilities as it either gives solutions similar to the p-median model, or it gives unstable solutions due to a non-concave objective function.

  • 49.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Human Geography.
    Rebreyend, Pascal
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Distance measure and the p-median problem in rural areas2012Report (Other academic)
    Abstract [en]

    The p-median model is used to locate P facilities to serve a geographically distributed population. Conventionally, it is assumed that the population patronize the nearest facility and that the distance between the resident and the facility may be measured by the Euclidean distance. Carling, Han, and Håkansson (2012) compared two network distances with the Euclidean in a rural region witha sparse, heterogeneous network and a non-symmetric distribution of thepopulation. For a coarse network and P small, they found, in contrast to the literature, the Euclidean distance to be problematic. In this paper we extend their work by use of a refined network and study systematically the case when P is of varying size (2-100 facilities). We find that the network distance give as gooda solution as the travel-time network. The Euclidean distance gives solutions some 2-7 per cent worse than the network distances, and the solutions deteriorate with increasing P. Our conclusions extend to intra-urban location problems.

  • 50.
    Carling, Kenneth
    et al.
    Dalarna University, School of Technology and Business Studies, Statistics.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Håkansson, Johan
    Dalarna University, School of Technology and Business Studies, Information Systems.
    Rebreyend, Pascal
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Distance measure and the p-median problem in rural areas2015In: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 226, no 1, 89-99 p.Article in journal (Refereed)
    Abstract [en]

    The p-median model is used to locate P facilities to serve a geographically distributed population. Conventionally, it is assumed that the population patronize the nearest facility and that the distance between the resident and the facility may be measured by the Euclidean distance. Carling, Han, and Håkansson (2012) compared two network distances with the Euclidean in a rural region with a sparse, heterogeneous network and a non-symmetric distribution of the population. For a coarse network and P small, they found, in contrast to the literature, the Euclidean distance to be problematic. In this paper we extend their work by use of a refined network and study systematically the case when P is of varying size (1-100 facilities). We find that the network distance give as good a solution as the travel-time network. The Euclidean distance gives solutions some 4-10 per cent worse than the network distances, and the solutions tend to deteriorate with increasing P. Our conclusions extend to intra-urban location problems.

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