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  • 1.
    Almasri, Abdullah
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    A Approach for Analysing the Fractional Difference Processes2006Konferensbidrag (Refereegranskat)
  • 2.
    Almasri, Abdullah
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Some aspects of wavelet analysis in time series2000Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 3.
    Almasri, Abdullah
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Testing for Periodicity and Trend in Long-Memory Processes2003Doktorsavhandling, monografi (Övrigt vetenskapligt)
  • 4.
    Almasri, Abdullah
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Andersson, Eva M
    Barregård, Lars
    A study of residential radon in Sweden using multilevel analysis2008Ingår i: Health Physics Journal, to appear 2008Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Swedish radon data set, consisting of more than 8000 measurements of residential radon levels in about 50% of the Swedish municipalities were analysed using a multilevel approach.

    The results were compared with those of a single-level analysis. We found that there was a significant variability between municipalities. The point estimates of the population mean radon levels were similar (geometric mean 60 Bq/m3 and arithmetic mean 106 Bq/m3).

    The analysis shows the advantages of multilevel modeling compared with a single-level OLS model.

    A single-level model results in too optimistic standard errors, about 25% of those of the multilevel

    model which can lead to erroneous conclusions.

    In a multilevel model including house type as a fixed effect (single-family house, row house, or apartment in multi-family house), the estimates of the fixed effect of house type were similar for the single-level and the multi-level models

  • 5.
    Almasri, Abdullah
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Hussain, S
    Holmquist, B
    Impact of the Periodicity and Trend on the FD Parameter Estimation2007Ingår i: Journal of Statistical Computation and Simulation. 2007, 77, 79-87Artikel i tidskrift (Refereegranskat)
  • 6.
    Almasri, Abdullah
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Locking, Håkan
    Shukur, Ghazi
    Testing for climate warming in Sweden during 1850-1999, using wavelets analysis2008Ingår i: Journal of Applied Statistics, 2008, vol. 35, issue 4, pages 431-443Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes an alternative approach for testing for the existence of trend among time series. The test method has been constructed using wavelet analysis which has the ability of decomposing a time series into low frequencies (trend) and high-frequency (noise) components. Under the normality assumption, the test is distributed as F. However, using generated empirical critical values, the properties of the test statistic have been investigated under different conditions and different types of wavelet. The Harr wavelet has shown to exhibit the highest power among the other wavelet types. The methodology here has been applied to real temperature data in Sweden for the period 1850-1999. The results indicate a significant increasing trend which agrees with the 'global warming' hypothesis during the last 100 years.

  • 7.
    Almasri, Abdullah
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Shukur, G.
    An Illustration of the Causality Relation between Government Spending and Revenue Using Wavelets Analysis on Finish Data2003Ingår i: Journal of Applied Statistics, 2003, 30, 571-584Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quarterly data for the period 1960:1 to 1997:2, conventional tests, a bootstrap simulation approach and a multivariate Rao's F-test have been used to investigate if the causality between government spending and revenue in Finland was changed at the beginning of 1990 due to future plans to create the European Monetary Union (EMU). The results indicate that during the period before 1990, the government revenue Granger-caused spending, while the opposite happened after 1990, which agrees better with Barro's tax smoothing hypothesis. However, when using monthly data instead of quarterly data for almost the same sample period, totally different results have been noted. The general conclusion is that the relationship between spending and revenue in Finland is still not completely understood. The ambiguity of these results may well be due to the fact that there are several time scales involved in the relationship, and that the conventional analyses may be inadequate to separate out the time scale structured relationships between these variables. Therefore, to investigate empirically the relation between these variables we attempt to use the wavelets analysis that enables us to separate out different time scales of variation in the data. We find that time scale decomposition is important for analysing these economic variables.

  • 8.
    Almasri, Abdullah
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Shukur, G
    Testing the Causal Relation between Sunspots and Temperature Using Wavelets Analysis2005Ingår i: Journal of Modern Applied Statistical Methods, 2005, 4, 134-139Artikel i tidskrift (Refereegranskat)
  • 9.
    Almasri, Abdullah
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Shukur, Ghazi
    Clustering Using Wavelet Transformation2008Ingår i: Handbook of Research on Cluster Theory / [ed] Charlie Karlsson, Edward Elgar , 2008Kapitel i bok, del av antologi (Refereegranskat)
  • 10.
    Andersson, Fredrik
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT.
    Prognostisering av Sveriges inflation: Med hjälp av ARIMA-modeller2007Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Syftet med min uppsats är att redogöra för de steg som krävs för att prognostisera den svenska inflationen med hjälp av Autoregressive Integrated Moving Average (ARIMA), för att sedan bestämma den modell som ger den bästa prognosen. Jag använder mig av månadsdata av Konsumentprisindex (KPI) som mått på inflation. För att man ska kunna prognostisera en tidsserie är det viktigt att den är stationär  och efter att ha utforskat korrelogram drar jag slutsatsen att dels en förstadifferens och dels en tolvmånadersdifferens måste tas för att kunna prognostisera KPI.   

    Jag följer Box-Jenkins-metodologin tämligen väl, där modellidentifikation, diagnostiska test och prognostisering är centrala begrepp.  Jag rankar de tio bästa modellerna enligt Bayesian Information Criterion (BIC) för att sedan utföra diagnostiska test på den bästa modellen i synnerhet och de andra modellerna i allmänhet. Slutligen utvärderas de olika modellerna bl.a. med hjälp av ”Root Mean Square Error” (RMSE). Den modell som bäst prognostiserar  inflationen  är en säsongsbetonad Moving Average  process  av order  ett förutom differentieringarna. 

  • 11.
    Appelgren, Jari
    Umeå universitet.
    Locally D-optimal Designs for Bivariate Logistic Regression2004Licentiatavhandling, monografi (Övrigt vetenskapligt)
  • 12. Beentjes, Casper
    et al.
    Di Bucchianico, Alessandro
    Hamster, Christian
    Kadu, Ajinkya
    Man, Irene
    Myerscough, Keith
    Regis, Marta
    Richardson, Omar
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap (from 2013).
    Equalizing the Cost of Health Insurance2017Ingår i: Proceedings of the 126th European Study GroupMathematics with Industry / [ed] Daan Crommelin, Stella Kapodistria, Guus Regts, Chris Stolk, Peter van de Ven, SWI , 2017, s. 29-49Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The Dutch government compensates health insurance companies when insuringindividuals who are estimated to have high health care costs. This is necessaryto avoid insurers not offering services to certain groups or not providing themwith a high quality of service. It is, however, unknown to what extent thedifferences in health care expenses by different groups of people are truly due toa poorer or better health status. We explore several statistical approaches thatfacilitate explaining the cause of these differences.

  • 13.
    Bergh, Daniel
    Karlstads universitet, Fakulteten för samhälls- och livsvetenskaper, Avdelningen för hälsa och miljö. Karlstads universitet, Fakulteten för humaniora och samhällsvetenskap (from 2013), Centrum för forskning om barns och ungdomars psykiska hälsa.
    Chi-Squared Test of Fit and Sample Size-A Comparison between a Random Sample Approach and a Chi-Square Value Adjustment Method2015Ingår i: Journal of Applied Measurement, ISSN 1529-7713, Vol. 16, nr 2, s. 204-217Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chi-square statistics are commonly used for tests of fit of measurement models. Chi-square is also sensitive to sample size, which is why several approaches to handle large samples in test of fit analysis have been developed. One strategy to handle the sample size problem may be to adjust the sample size in the analysis of fit. An alternative is to adopt a random sample approach. The purpose of this study was to analyze and to compare these two strategies using simulated data. Given an original sample size of 21,000, for reductions of sample sizes down to the order of 5,000 the adjusted sample size function works as good as the random sample approach. In contrast, when applying adjustments to sample sizes of lower order the adjustment function is less effective at approximating the chi-square value for an actual random sample of the relevant size. Hence, the fit is exaggerated and misfit under-estimated using the adjusted sample size function. Although there are big differences in chi-square values between the two approaches at lower sample sizes, the inferences based on the p-values may be the same.

  • 14.
    Bergh, Daniel
    Karlstads universitet, Fakulteten för humaniora och samhällsvetenskap (from 2013), Centrum för forskning om barns och ungdomars psykiska hälsa.
    Sample Size and Chi-Squared Test of Fit: A comparison Between a Random Sample Approach and a Chi-Square Value Adjustment Method Using Swedish Adolescent Data2015Ingår i: Pacific Rim Objective Measurement Symposium (PROMS) 2014 Conference Proceedings: Rasch and the Future / [ed] Zhang, Quan., & Yang, Hong. (Eds.), Springer Berlin/Heidelberg, 2015, s. 197-211Konferensbidrag (Refereegranskat)
    Abstract [en]

    Background: Significance tests are commonly sensitive to sample size, and Chi-Squared statistics is not an exception. Nevertheless, Chi-Squared statistics are commonly used for test of fit of measurement models. Thus, for analysts working with very large (or very small) sample sizes this may require particular attention. However, several different approaches to handle a large sample size in test of fit analysis have been developed. Thus, one strategy may be to adjust the fit statistic to correspond to an equivalent sample of different size. This strategy has been implemented in the RUMM2030 software. Another strategy may be to adopt a random sample approach.

    Aims: The RUMM2030 Chi-Square value adjustment facility has been available for a long time, but still there are few studies describing the empirical consequences of adjusting the sample to correspond to a smaller effective sample size in the statistical analysis of fit. Alternatively a random sample approach could be adopted in order to handle the large sample size problem. The purpose of this study was to analyze and compare these two strategies as test of fit approximations, using Swedish adolescent data. 

    Sample:The analysis is based on the survey Young in Värmland which is a paper-and-pencil based survey conducted recurrently since 1988 targeting all adolescent in school year 9 residing the county of Värmland, Sweden. So far, more than 20,000 individuals have participated in the survey. In the analysis presented here, seven items based on the adolescents, experiences of the school environment were subjected to analysis, in total 21,088 individuals.

    Methods: For the purposes of this study, the original sample size was adjusted to several different effective samples using the RUMM2030 adjustment function, in the test of fit analysis. In addition, 10 random samples for each sample size were drawn from the original sample, and averaged Chi-Square values calculated. The Chi-Square values obtained using the two strategies were compared.

    Results: Given the original sample of 21,000, adjusting to samples 5,000 or larger, the RUMM2030 adjustment facility work as well as a random sample approach. In contrast, when adjusting to lower samples the adjustment function is less effective in approximating the Chi-Square value for an actual random sample of the relevant size. Hence, fit is exaggerated and misfit under estimated using the adjustment function, in particular is that true for fitting but not misfitting items.  

    Conclusion: Even though the inferences based on p-values may be the same despite big Chi-Square value differences between the two approaches, the danger of using fit statistics mechanically cannot be enough stressed. Neither the adjustment function, nor the random sample approach is sufficient in evaluating model fit, instead several complementing methods should be used.

     

  • 15.
    Bernhoff, Niclas
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap (from 2013).
    Discrete Velocity Models for Polyatomic Molecules Without Nonphysical Collision Invariants2018Ingår i: Journal of statistical physics, ISSN 0022-4715, E-ISSN 1572-9613, Vol. 172, nr 3, s. 742-761Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An important aspect of constructing discrete velocity models (DVMs) for the Boltzmann equation is to obtain the right number of collision invariants. Unlike for the Boltzmann equation, for DVMs there can appear extra collision invariants, so called spurious collision invariants, in plus to the physical ones. A DVM with only physical collision invariants, and hence, without spurious ones, is called normal. The construction of such normal DVMs has been studied a lot in the literature for single species, but also for binary mixtures and recently extensively for multicomponent mixtures. In this paper, we address ways of constructing normal DVMs for polyatomic molecules (here represented by that each molecule has an internal energy, to account for non-translational energies, which can change during collisions), under the assumption that the set of allowed internal energies are finite. We present general algorithms for constructing such models, but we also give concrete examples of such constructions. This approach can also be combined with similar constructions of multicomponent mixtures to obtain multicomponent mixtures with polyatomic molecules, which is also briefly outlined. Then also, chemical reactions can be added.

  • 16.
    Berthold, Stefan
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap.
    Inter-temporal Privacy Metrics2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Informational privacy of individuals has significantly gained importance after information technology has become widely deployed. Data, once digitalised, can be copied, distributed, and long-term stored at negligible costs. This has dramatic consequences for individuals that leave traces in the form of personal data whenever they interact with information technology, for instance, computers and phones; or even when information technology is recording the personal data of aware or unaware individuals. The right of individuals for informational privacy, in particular to control the flow and use of their personal data, is easily undermined by those controlling the information technology.

    The objective of this thesis is to study the measurement of informational privacy with a particular focus on scenarios where an individual discloses personal data to a second party which uses this data for re-identifying the individual within a set of other individuals. We contribute with privacy metrics for several instances of this scenario in the publications included in this thesis, most notably one which adds a time dimension to the scenario for modelling the effects of the time passed between data disclosure and usage. The result is a new framework for inter-temporal privacy metrics.

  • 17.
    Berthold, Stefan
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap.
    Lundin, Reine
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för matematik och datavetenskap.
    Re-identification revisitedManuskript (preprint) (Övrigt vetenskapligt)
  • 18.
    Cirillo, Emilio N. M.
    et al.
    Sapienza Universit`a di Roma.
    Muntean, Adrian
    Eindhoven University of Technology.
    Can cooperation slow down emergency evacuations?2012Ingår i: Comptes rendus. Mecanique, ISSN 1631-0721, E-ISSN 1873-7234, Vol. 340, nr 9, s. 625-628Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the motion of pedestrians through obscure corridors where the lack of visibility hides the precise position of the exits. Using a lattice model, we explore the effects of cooperation on the overall exit flux (evacuation rate). More precisely, we study the effect of the buddying threshold (of no–exclusion per site) on the dynamics of the crowd. In some cases, we note that if the evacuees tend to cooperate and act altruistically, then their collective action tends to favor the occurrence of disasters.

  • 19.
    Cirillo, Emilio N.M.
    et al.
    Università di Roma “La Sapienza”.
    Colangeli, Matteo
    Gran Sasso Science Institute.
    Muntean, Adrian
    Eindhoven University of Technology.
    Does communication enhance pedestrians transport in the dark?2016Ingår i: Comptes rendus. Mecanique, ISSN 1631-0721, E-ISSN 1873-7234, Vol. 344, nr 1, s. 19-23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the motion of pedestrians through an obscure tunnel where the lack of visibility hides the exits. Using a lattice model, we explore the effects of communication on the effective transport properties of the crowd of pedestrians. More precisely, we study the effect of two thresholds on the structure of the effective nonlinear diffusion coefficient. One threshold models pedestrian communication efficiency in the dark, while the other one describes the tunnel capacity. Essentially, we note that if the evacuees show a maximum trust (leading to a fast communication), they tend to quickly find the exit and hence the collective action tends to prevent the occurrence of disasters.

  • 20. Cirillo, Emilio N.M.
    et al.
    Muntean, Adrian
    Eindhoven University of Technology.
    Dynamics of pedestrians in regions with no visibility: A lattice model without exclusion2013Ingår i: Physica A: Statistical Mechanics and its Applications, ISSN 0378-4371, Vol. 392, nr 17, s. 3578-3588Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the motion of pedestrians through obscure corridors where the lack of visibility (due to smoke, fog, darkness, etc.) hides the precise position of the exits. We focus our attention on a set of basic mechanisms, which we assume to be governing the dynamics at the individual level. Using a lattice model, we explore the effects of non-exclusion on the overall exit flux (evacuation rate). More precisely, we study the effect of the buddying threshold (of no-exclusion per site) on the dynamics of the crowd and investigate to which extent our model confirms the following pattern revealed by investigations on real emergencies: If the evacuees tend to cooperate and act altruistically, then their collective action tends to favor the occurrence of disasters. The research reported here opens many fundamental questions and should be seen therefore as a preliminary investigation of the very complex behavior of the people and their motion in dark regions.

  • 21.
    Cirillo, E.N.M.
    et al.
    Univ Roma La Sapienza, Dipartimento Sci Base & Applicate Ingn, Rome, Italy.
    Krehel, O.
    Eindhoven Univ Technol, Inst Complex Mol Syst, Eindhoven, Netherlands.
    Muntean, Adrian
    Eindhoven Univ Technol, Inst Complex Mol Syst.
    van Santen, R.
    Eindhoven Univ Technol, Inst Complex Mol Syst, Eindhoven, Netherlands.
    Sengar, A.
    Indian Inst Technol Delhi, Delhi, India.
    Residence time estimates for asymmetric simple exclusion dynamics on strips2015Ingår i: Physica A: Statistical Mechanics and its Applications, ISSN 0378-4371, E-ISSN 1873-2119, Vol. 442, s. 436-457Artikel i tidskrift (Refereegranskat)
  • 22.
    Corbetta, Alessandro
    et al.
    Eindhoven University of Technolology; Politecnio di Torino.
    Muntean, Adrian
    Eindhoven University of Technolology.
    Vafayi, Kiamars
    Eindhoven University of Technolology.
    Parameter estimation of social forces in pedestrian dynamics models via a probabilistic method2015Ingår i: Mathematical Biosciences and Engineering, ISSN 1547-1063, E-ISSN 1551-0018, Vol. 12, nr 2, s. 337-356Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Focusing on a specific crowd dynamics situation, including real life experiments and measurements, our paper targets a twofold aim: (1) we present a Bayesian probabilistic method to estimate the value and the uncertainty (in the form of a probability density function) of parameters in crowd dynamic models from the experimental data; and (2) we introduce a fitness measure for the models to classify a couple of model structures (forces) according to their fitness to the experimental data, preparing the stage for a more general model-selection and validation strategy inspired by probabilistic data analysis. Finally, we review the essential aspects of our experimental setup and measurement technique.

  • 23.
    Forsberg, Niklas
    Karlstads universitet, Fakulteten för humaniora och samhällsvetenskap (from 2013), Handelshögskolan.
    What affects the tear strength of paperboard?: Consequences of unbalance in a designed experiment2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This essay covers a designed experiment on paperboard where the quality under study is tear strength alongside and across.

    The objective is to examine what consequences the loss of balance in a designed experiment has on the explanatory power of the proposed empirical model. As did happen, the trial plan didn’t go as planned when the first run caused a disruption of the paperboard in the machine. Decision from the company was to raise the low level of one of the design factors to prevent this from happening again. The consequence of this is an alteration of the design during ongoing experimentation. This in turn affects what analysis approaches are appropriate for the problem.

    Three different approaches for analyzing the data are presented, each with different propositions on how to deal with the complication that occurred. The answer to the research question is that the ability of the empirical model to discover significant effects is moderately weakened by the loss of one run (out of eight total). The price payed for retrieving less information from the experiment is that the empirical model, for tear strength across, doesn’t deem the effects significant at the same level as for the candidate model with eight runs. Instead of concluding that the main effect of  and the interaction effect  is significant at the 2%- and 4%-level, respectively, we must now settle with deeming them significant at the 6%- and 7%-level. 

  • 24. Harley, M
    et al.
    Mohammed, A M
    Hussain, S
    Yates, J
    Almasri, Abdullah
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Was Rodney Ledward a statistical outlier? Retrospective analysis using hospital data to identify gynaecologists performance2005Ingår i: British Medical Journal, 2005, 330, 929Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objectives: To investigate whether routinely collected data from hospital episode statistics could be used to identify the gynaecologist Rodney Ledward, who was suspended in 1966 and was the subject of the Ritchie inquiry into quality and practice within the NHS.

    Design A mixed scanning approach was used to identify seven variables from hospital episode statistics that were likely to be associated with potentially poor performance. A blinded multivariate analysis was undertaken to determine the distance (known as the Mahalanobis distance) in the seven indicator multidimensional space that each consultant was from the average consultant in each year. The change in Mahalanobis distance over time was also investigated by using a mixed effects model.



    Setting: NHS hospital trusts in two English regions, in the five years from 1991-2 to 1995-6.



    Population: Gynaecology consultants (n = 143) and their hospital episode statistics data.



    Main outcome measure Whether Ledward was a statistical outlier at the 95% level.



    Results: The proportion of consultants who were outliers in any one year (at the 95% significance level) ranged from 9% to 20%. Ledward appeared as an outlier in three of the five years. Our mixed effects (multi-year) model identified nine high outlier consultants, including Ledward.



    Conclusion: It was possible to identify Ledward as an outlier by using hospital episode statistics data. Although our method found other outlier consultants, we strongly caution that these outliers should not be overinterpreted as indicative of "poor" performance. Instead, a scientific search for a credible explanation should be undertaken, but this was outside the remit of our study. The set of indicators used means that cancer specialists, for example, are likely to have high values for several indicators, and the approach needs to be refined to deal with case mix variation. Even after allowing for that, the interpretation of outlier status is still as yet unclear. Further prospective evaluation of our method is warranted, but our overall approach may be potentially useful in other settings, especially where performance entails several indicator variables.

  • 25. Hussain, S
    et al.
    Elbergali, A
    Almasri, Abdullah
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Parsimonious Modelling, Testing and Forecasting of Long-Range Dependence in Wind Speed2004Ingår i: Environmetrics, 2004, 15, 155-171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Detecting and estimating long-range dependence are important in the analysis of many environmental time series. This article proposes a periodogram roughness (PR) estimator and describes its uses for testing and estimating the dependence structure. Asymptotic critical values are generated for performing the test, and special attention is given to investigating the properties of the PR regarding size and power. The conventional short-memory models, such as the autoregressive (AR), are shown to be less parsimonious. Forecasting errors of both fractional Gaussian noise (FGN) and fractional autoregressive moving average (FARMA) are investigated by conducting simulation studies. In addition to the PR, maximum likelihood (ML) and semi-parametric (SP) estimators are used and evaluated. Our results have shown that more accurate forecasted points are obtained when using the fractional forecasting. The methods are illustrated using Swedish wind speed data

  • 26. Hussain, S.
    et al.
    Mohamed, M. A.
    Holder, R.
    Almasri, Abdullah
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Shukur, G.
    Performance Evaluation Based on the Robust Mahalanobis Distance and Multilevel Modeling Using Two New Strategies2008Ingår i: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, Vol. 37, nr 10, s. 1966-1980Artikel i tidskrift (Refereegranskat)
  • 27.
    Klockare, Mikael
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Logit, oddskvot och sannolikhet: En analys av multinomial logistisk regression2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Den här uppsatsen inleds med att studera de moment som används för multinomial logistisk regression och hur resultaten mäts. Teorin tar sin avsats i den binomiala logistiska regression, för att stegvis ta sig vidare till den multinomiala logistiska regressionen. Begreppen logit, oddskvoten och sannolikheterna förtydligas, effekterna av de oberoende variablerna diskuteras och kopplingen till vanlig linjär regression åskådliggörs. Det blir även en fördjupning av matematiken bakom den logistiska funktionen.

    Därefter tillämpas den multinomial logistisk regressionsanalysen med ett praktiskt exempel. Analysmodellen är användbar inom flertalet områden och den här uppsatsen ligger inom ramen för sportanalys. Matchstatistik från ishockey och närmare bestämt Örebro Hockeys matcher från säsongerna 2012/13 till 2017/18 nyttjas och den slutgiltiga modellen använder sig av tre förklarande variabler. Resultatet visar att utfallet efter ordinarie tid kan förklaras till 60,9% med hjälp av matchstatistiken, vilket tyder på att den multinomiala regressionsmodellen presterar likvärdigt med andra metoder som tillämpar kategorisk dataanalys inom sportanalys.

  • 28. Lilford, Richard
    et al.
    Girling, Alan
    Stevens, Andrew
    Almasri, Abdullah
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för nationalekonomi och statistik.
    Mohammed, Mohammed A
    Braunholtz, David
    Adjusting for treatment refusal in rationing decisions2006Ingår i: BMJ 2006;332;542-544Artikel i tidskrift (Refereegranskat)
  • 29.
    Mossberg, Magnus
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik.
    A statistical inference method for a subset of long-range dependent FARIMA processes2012Ingår i: Statistical Signal Processing Workshop (SSP), 2012 IEEE, IEEE conference proceedings, 2012, s. 456-459Konferensbidrag (Refereegranskat)
    Abstract [en]

    A subset of long-range dependent FARIMA processes is considered. A method for estimating the parameter that describes the long-range dependency of such a process is suggested. The method is based on an asymptotic expression for the covariance function of the process and gives a closed form solution by means of a weighted linear least squares estimate. The variance of the estimate given by themethod is analyzed and, at the same time, the optimal choice of the weighting is expressed. A numerical illustration of the method and the material in the paper is provided

  • 30.
    Mossberg, Magnus
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik.
    Analysis of moments based methods for fractional Gaussian noise estimation2012Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, nr 7, s. 3823-3827Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fractional Gaussian noise, given as the increment of fractional Brownian motion, is a stationary Gaussian process characterized by the Hurst parameter. In the paper, moments based estimators of the Hurst parameter are presented and analyzed with respect to asymptotic variance

  • 31.
    Mossberg, Magnus
    et al.
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik.
    Mossberg, Eva
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för matematik.
    A Note on Parameter Estimation in Lamperti Transformed Fractional Ornstein-Uhlenbeck Processes2012Ingår i: IFAC Proceedings Volumes / [ed] Kinnaert, Michel, Elsevier, 2012, Vol. 45/16, s. 1067-1072Konferensbidrag (Refereegranskat)
  • 32.
    Muntean, Stela Andrea
    et al.
    Eindhoven University of Technology, Netherlands; Dutch Polymer Institute, Netherlands.
    Kemper, Marijn
    Eindhoven University of Technology, Netherlands; Dutch Polymer Institute, Netherlands.
    Van Ijzendoorn, L. J.
    Eindhoven University of Technology, Netherlands.
    Lyulin, A. V.
    Eindhoven University of Technology, Netherlands.
    Roughness and ordering at the interface of oxidized polystyrene and water2011Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, nr 14, s. 8678-8686Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the first time, atomistically detailed molecular dynamics calculations revealed molecular ordering of the water-oxidized atactic polystyrene (aPS) interface. Both ordering of the water molecules and the phenyl rings occur. In addition, the natural roughness of the surface has been simulated and compared to experimental values. The composition of the simulated aPS films is based on spin-coated aPS films that have been oxidized and characterized experimentally. The aPS surfaces are oxidized with ultraviolet-ozone radiation and have been characterized by XPS, AFM, and water contact angle measurements. XPS measurements show that the oxygen content in the sample increases rapidly with exposure and reaches saturation near 24 at. % of oxygen. The molecular dynamics simulations show smoothening of an hydrophobic aPS surface upon transition from vacuum to water. The smoothening decreases with increasing hydrophilicity. The calculations reveal ordering of oxidized phenyl rings for aPS surfaces in water. The order increases with increasing hydrophilicity. Additionally, we investigated the water structure near the aPS-water interface as a function of the surface hydrophilicity. With increasing hydrophilicity, the density of water at the aPS-water interface increases. The water density profile is steeper in the presence of hydrophobic aPS. The water shows an ordered layer near both the hydrophobic and hydrophilic surfaces; the position of this layer shifts toward the interface with increasing hydrophilicity. © 2011 American Chemical Society.

  • 33.
    Söderström, Torsten
    et al.
    Uppsala University.
    Irshad, Yasir
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik.
    Mossberg, Magnus
    Karlstads universitet, Fakulteten för teknik- och naturvetenskap, Avdelningen för fysik och elektroteknik.
    Zheng, Wei Xing
    University of Western Sydney.
    Accuracy analysis of a covariance matching method for continuous-time errors-in-variables system identification2012Ingår i: : IFAC Proceedings Volumes, Elsevier, 2012, Vol. 45, s. 1383-1388Konferensbidrag (Refereegranskat)
  • 34.
    Tilevik, Andreas
    Karlstads universitet, Fakulteten för humaniora och samhällsvetenskap (from 2013), Handelshögskolan.
    Evaluation of clustering methods for analyzing drug cytokine profiles2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Huvudsyftet med denna studie var att utvärdera olika klustringsmetoder för att analysera data hämtade från en läkemedelsstudie där cytokinprofiler hade genererats från 23 olika läkemedel. Hierarkisk klustring användes eftersom antal kluster inte var förutbestämt. Olika distansmått och s.k. länkfunktioner utvärderades för hierarkisk klustring. Utvärderingen av de olika distansmåtten visade att Pearsons korrelationskoefficient lämpade sig bäst vid klustring av de olika läkemedlen eftersom likheter i mönster var viktigare än de faktiska mätvärdena. Även fyra länkfunktioner för att slå samman kluster utvärderades. Den länkfunktion som beräknade medelavståndet mellan objektens kluster visade sig vara den optimala metoden baserat på robusthet och korrelation mellan avstånden i dendrogramet och avstånden i distansmatrisen. Genom att använda hierarkisk klustring baserat på Pearsons korrelationskoefficient och medelavstånd så kunde ett antal intressanta läkemedelsgrupper identifieras. De s.k. JAK-inhibitorerna grupperades i ett distinkt kluster medan calcineurin inhibitorerna återfanns i ett robust kluster tillsammans med proteinkinasinhibitorer. Denna studie visar att klustring av läkemedel baserat på cytokinprofiler kan erbjuda viktig information som beslutstöd för framtida projekt inom läkemedelsutveckling, samt att avstånd baserade på Pearsons korrelationskoefficient och att en länkfunktion som beräknar medelavstånd lämpar sig bäst för den här typen av data.  

  • 35.
    Uggla, Claes
    et al.
    Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), Institutionen för ingenjörsvetenskap och fysik (from 2013).
    Wainwright, John
    University of Waterloo, Canada.
    Second order cosmological perturbations: simplified gauge change formulas2019Ingår i: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 36, nr 3, s. 1-19, artikel-id 035004Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we present a new formulation of the change of gauge formulas in second order cosmological perturbation theory which unifies and simplifies known results. Our approach is based on defining new second order scalar perturbation variables by adding a multiple of the square of the corresponding first order variables to each second order variable. A bonus is that these new perturbation variables are of broader significance in that they also simplify the analysis of second order scalar perturbations in the super-horizon regime in a number of ways, and lead to new conserved quantities.

1 - 35 av 35
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