Testing the Assumption of Sample Invariance of Item Difficulty Parameters in the Rasch Rating Scale Model Testing the Assumption of Sample Invariance of Item Difficulty Parameters in the Rasch Rating Scale Model
The study used three methods to assess variation: (a) the between-fit statistic, (b) confidence intervals around the mean of the estimates and (c) a general linear model. The general linear model used the person residual statistic from the Winstepsâ€™ person output file as a dependent variable with year, gender and type of major as independent variables.
Results of the study support the invariant nature of the item difficulty estimates when polytomous data from the alumni questionnaire is used. The analysis found comparable results (within sampling error) for the between-fit statistics and the general linear model. The confidence interval method was limited in its usefulness due to small confidence bands and the limitation of the plots. The linear model offered the most valuable data in that it provides methods to not only detect the existence of variation but to assess the relative magnitude of the variation from different sources.
Recommendations for future research include studies regarding the impact of sample size on the between-fit statistic and confidence intervals as well as the impact of large amounts of systematic missing data on the item parameter estimates.
School:Brigham Young University
School Location:USA - Utah
Source Type:Master's Thesis
Keywords:rasch invariance polytomous rating scale item difficulties
Date of Publication:07/20/2007