A MODEL-BASED STANDARDIZATION APPROACH THAT SEPARATES TRUE BIAS DIF FROM GROUP ABILITY DIFFERENCES AND DETECTS TEST BIAS/DTF AS WELL AS ITEM BIAS/DIF/

A model-based modification (SIBTEST) of the standardization index base d upon a multidimensional IRT bias modeling approach is presented that detects and estimates DIF or item bias simultaneously for several ite ms. A distinction between DIF and bias is proposed. SIBTEST detects bi as/DIF without the usual Type 1 error inflation due to group target ab ility differences. In simulations, SIBTEST performs comparably to Mant el-Haenszel for the one item case. SIBTEST investigates bias/DIF for s everal items at the test score level (multiple item DIF called differe ntial test functioning: DTF), thereby allowing the study of test bias/ DIF, in particular bias/DIF amplification or cancellation and the cogn itive bases for bias/DIF.