Possible Factors Which May Impact Kernel Equating of Mixed-Format Tests

Mixed-format tests contain items with different formats such as dichotomously scored and polytomously scored items. The aim of this study was to examine the impact of item discrimination, sample size, and proportion of polytomously scored items on item response theory (IRT) kernel equating of mixed-format tests under the equivalent groups design. A simulation study was performed to examine the aim. The results from the simulation study showed that the percent relative errors were low and stable for all conditions, whereas differences in standard errors and equated values where found for the conditions with different sample sizes and item discriminations. Also, the standard errors were higher when the proportion of polytomously scored items in the test where higher.