ltm: An R package for latent variable modeling and item response theory analyses

JSS Journal of Statistical Software November 01/2006; 17.

ABSTRACT The R package ltm has been developed for the analysis of multivariate dichotomous and polytomous data using latent variable models, under the Item Response Theory ap-proach. For dichotomous data the Rasch, the Two-Parameter Logistic, and Birnbaum's Three-Parameter models have been implemented, whereas for polytomous data Seme-jima's Graded Response model is available. Parameter estimates are obtained under marginal maximum likelihood using the Gauss-Hermite quadrature rule. The capabilities and features of the package are illustrated using two real data examples.

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    ABSTRACT: Item response theory (IRT) models are a class of statistical models used by researchers to describe the response behaviors of individuals to a set of categorically scored items. The most common IRT models can be classified as generalized linear fixed- and/or mixed-effect models. Although IRT models appear most often in the psychological testing literature, researchers in other fields have successfully utilized IRT-like models in a wide variety of applications. This paper discusses the three major methods of estimation in IRT and develops R functions utilizing the built-in capabilities of the R environment to find the marginal maximum likelihood estimates of the generalized partial credit model. The currently available R packages ltm is also discussed.
    Journal of statistical software 01/2007; 20(i10). · 3.80 Impact Factor
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    ABSTRACT: This research includes the design of a questionnaire for evaluating cultural coexistence in secondary education classrooms (Berrocal, Olmedo & Olmos, 2014; Olmedo et al., 2014), as well as the comparison of its psychometric properties in a multicultural population of schools in southern Spain. An attempt is made to create a valid, reliable and useful tool for teachers to measure conflict situations in the classroom, as well as understanding the nature of the conflict from the point of view of all those involved. The metric aspects show a maximized content and construct validity (Muñiz, 2010) using a Structural Equation Model (SEM) and Confirmatory Factor Analysis (CFA) analysis, checking and modifying its model by Wald and Lagrange indicators (Bentler, 2007), to obtain the most adjusted model to the theoretical and goodness criteria.
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    ABSTRACT: Background The WHOQOL-OLD is an instrument for the assessment of subjective quality of life in elderly people. It is based on the WHO definition of quality of life and is available in more than 20 languages. However, in most countries, the psychometric properties of the WHOQOL-OLD have been assessed only on the basis of small local samples and not in representative studies. In this study, the psychometric properties of the WHOQOL-OLD are evaluated based on a representative sample of Germany¿s elderly population.Methods Face-to-face interviews with 1133 respondents from the German population aged 60 years and older were conducted. Quality of life was assessed by means of the WHOQOL-BREF, the WHOQOL-OLD and the SF12. Moreover, the GDS, the DemTect and the IADL were applied for the assessment of depressive symptoms, cognitive capacities and capacity for carrying out daily activities. Psychometric properties of the WHOQOL-OLD were evaluated by means of classical and probabilistic test theory, confirmatory factor analysis and multivariate regression model.ResultsCronbach¿s alpha was found to be above 0.85 for four and above .75 for two of the six facets of the WHOQOL-OLD. IRT analyses indicated that all items of the WHOQOL-OLD contribute considerably to the measurement of the associated facets. While the six-facet structure of the WHOQOL-OLD was well supported by the results of the confirmatory factor analysis, a common latent factor for the WHOQOL-OLD total scale could not be identified. Correlations with other quality of life measures and multivariate regression models with GDS, IADL and the DemTect indicate a good criterion validity of all six WHOQOL-OLD facets.Conclusions Study results confirm that the good psychometric properties of the WHOQOL-OLD that have been found in international studies could be replicated in a representative study of the German population. These results suggest that the WHOQOL-OLD is an instrument that is well suited to identify the needs and the wishes of an aging population.
    Health and Quality of Life Outcomes 09/2014; 12(1):105. DOI:10.1186/s12955-014-0105-4 · 2.10 Impact Factor


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