Application of Sampling Variance of Item Response Theory Parameter Estimates in Detecting Outliers in Common Item Equating.

Abstract

In common item equating, the existence of item outliers may impact the accuracy of equating results and bring significant ramifications to the validity of test score interpretations. Therefore, common item equating should involve a screening process to flag outlying items and exclude them from the common item set before equating is conducted. The current simulation study demonstrated that the sampling variance associated with the item response theory (IRT) item parameter estimates can help detect outliers in the common items under the 2-PL and 3-PL IRT models. The results showed the proposed sampling variance statistic (SV) outperformed the traditional displacement method with cutoff values of 0.3 and 0.5 along a variety of evaluation criteria. Based on the favorable results, item outlier detection statistics based on estimated sampling variability warrant further consideration in both research and practice.