Sökning: "Marie Wiberg"

Visar resultat 1 - 5 av 13 avhandlingar innehållade orden Marie Wiberg.

  1. 1. Computerized achievement tests : sequential and fixed length tests

    Författare :Marie H. Wiberg; Hans Nyquist; Ulf Olsson; Umeå universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; Statistics; item respons theory; sequential analysis; statistical inference; power; optimal design; simulations; Statistik; Statistics; Statistik; Statistics; statistik;

    Sammanfattning : The aim of this dissertation is to describe how a computerized achivement test can be constructed and used in practice. Throughout this dissertation the focus is on classifying the examinees into masters and non-masters depending on their ability. However, there has been no attempt to estimate their ability. LÄS MER

  2. 2. Contributions to Kernel Equating

    Författare :Björn Andersson; Fan Yang-Wallentin; Marie Wiberg; Alina A. von Davier; Jorge González; Uppsala universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; observed-score test equating; item response theory; R; equipercentile equating; asymptotic standard errors; non-equivalent groups with anchor test design; Statistics; Statistik;

    Sammanfattning : The statistical practice of equating is needed when scores on different versions of the same standardized test are to be compared. This thesis constitutes four contributions to the observed-score equating framework kernel equating. LÄS MER

  3. 3. Observed score equating with covariates

    Författare :Kenny Bränberg; Marie Wiberg; Xavier de Luna; Dag Sörbom; Umeå universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; Equating; observed score equating; true scores; item response theory; linear equating function; equipercentile equating; kernel equating; covariates; linear regression; mean squared error; Statistics; Statistik; Statistics; statistik;

    Sammanfattning : In test score equating the focus is on the problem of finding the relationship between the scales of different test forms. This can be done only if data are collected in such a way that the effect of differences in ability between groups taking different test forms can be separated from the effect of differences in test form difficulty. LÄS MER

  4. 4. Trace analysis of dioxins and dioxin-like PCBs using comprehensive two-dimensional gas chromatography with electron capture detection

    Författare :Conny Danielsson; Peter Haglund; Karin Wiberg; Jean-Marie Dimandja; Umeå universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; Comprehensive two-dimensional gas chromatography; GC × GC; µECD; PCDDs; PCDFs; dioxins; dioxin-like PCBs; Pressurized liquid extraction; PLE; PLE-C; food; feed; fly ash; soil; Environmental chemistry; Miljökemi;

    Sammanfattning : Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), two groups of struc-turally related chlorinated aromatic hydrocarbons, generally referred to as “dioxins” are of great concern due to their extreme toxicity and presence in all compartments of the environment. Since they occur at very low levels, their analysis is complex and challenging, and there is a need for cost-efficient, reliable and rapid analytical alternatives to the expensive methods in-volving use of gas chromatography high-resolution mass spectrometry (GC-HRMS). LÄS MER

  5. 5. Selection of smoothing parameters with application in causal inference

    Författare :Jenny Häggström; Xavier de Luna; Marie Wiberg; Yanyuan Ma; Umeå universitet; []
    Nyckelord :NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; NATURAL SCIENCES; Smoothing parameter selection; Nonparametric regression; Semiparametric additive model; Double smoothing; Causal inference; BMI; Divorce; Statistics; Statistik; Statistics; statistik;

    Sammanfattning : This thesis is a contribution to the research area concerned with selection of smoothing parameters in the framework of nonparametric and semiparametric regression. Selection of smoothing parameters is one of the most important issues in this framework and the choice can heavily influence subsequent results. LÄS MER