EFFECTS OF LINKING METHODS ON DETECTION OF DIF

Studies of differential item functioning under item response theory require that item parameter estimates be placed on the same metric before comparisons can be made. The present study compared the effects of three methods for linking metrics: a weighted mean and sigma method (WMS); the test characteristic curve method (TCC); and the minimum chi-square method (MCS), on detection of differential item functioning. Both iterative and noniterative linking procedures were compared for each method. Results indicated that detection of differentially functioning items following linking via the test characteristic curve method gave the most accurate results when the sample size was small. When the sample size was large, results for the three linking methods were essentially the same. Iterative linking provided an improvement in detection of differentially functioning items over noniterative linking particularly with the .05 alpha level. The weighted mean and sigma method showed greater improvement with iterative linking than either the test characteristic curve or minimum chi-square method.