Effect of Sample Size Ratio and Model Misfit When Using the Difficulty Parameter Differences Procedure to Detect DIF |
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| Authors: | Ángela I Berrío Juana Gómez-Benito |
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| Institution: | 1. Universidad Nacional de Colombia-Sede Bogotá, Bogotá, Colombia;2. University of Barcelona, Barcelona Spain;3. University of Barcelona, Barcelona Spain |
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| Abstract: | This study examined the effect of sample size ratio and model misfit on the Type I error rates and power of the Difficulty Parameter Differences procedure using Winsteps. A unidimensional 30-item test with responses from 130,000 examinees was simulated and four independent variables were manipulated: sample size ratio (20/100/250/500/1000); model fit/misfit (1 PL and 3PLc =. 15 models); impact (no difference/mean differences/variance differences/mean and variance differences); and percentage of items with uniform and nonuniform DIF (0%/10%/20%). In general, the results indicate the importance of ensuring model fit to achieve greater control of Type I error and adequate statistical power. The manipulated variables produced inflated Type I error rates, which were well controlled when a measure of DIF magnitude was applied. Sample size ratio also had an effect on the power of the procedure. The paper discusses the practical implications of these results. |
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| Keywords: | DIF Difficulty Parameter Differences procedure model misfit sample size ratio Winsteps |
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