Comparison of Unidimensional and Multidimensional Models Based on Item Response Theory in Terms of Both Variables of Test Length and Sample Size

The purpose of this study is to compare unidimensional and multidimensional item response models under different test length and sample size situations based on Turkish language test data. Sample size and test length were manipulated as independent variables in this study. Test data collected from eight grade primary school students (n=1516). The findings suggested that item and ability parameters estimated under multidimensional IRT, have less error scores and reached more precise measurement and model data fits are in favour of multidimensional IRT. Also, manipulation of sample size and test length has no positive effect on model data fit under unidimensional IRT, but longer tests and larger samples decreases error estimation and more sensitive measurement results under multidimensional IRT.