Theoretically preferred item response theory (IRT) bias detection procedures were applied to both a mathematics achievement and vocabulary test. The data were from black seniors and white seniors on the High School and Beyond data files. We wished to account for statistical artifacts by conducting cross-validation or replication studies. Therefore, each analysis was repeated on randomly equivalent samples of blacks and whites (n's=1500). Furthermore, to establish a baseline for judging bias indices that might be attributable only to sampling fluctuations, bias analyses were conducted comparing randomly selected groups of whites. Also, to assess the effect of mean group differences on the appearance of bias, pseudo-ethnic groups were created, i.e., samples of whites were selected to simulate the average black-white difference. The validity and sensitivity of the IRT bias indices were supported by several findings. The pattern of between study correlations showed high consistency for parallel ethnic analyses where bias was plausibly present. Also, the indices met the discriminant validity test. Overall the sums-of-squares statistics (weighted by the inverse of the variance errors) were judged to be the best indices for quantifying item characteristic curve differences between groups. (PN)