Order effects in the IAT

We demonstrate that the IAT is crucially influenced by the order in which the two IAT-blocks are administered. In three studies the IAT-effect is shown to change in magnitude and sign when the order of the ‘compatible’ and the ‘incompatible’ block is reversed. Order effects are caused by cognitive inertia, the difficulty to switch from one categorization rule to another categorization rule. Cognitive inertia distorts correlations between IAT-scores and other variables. While the common practice of counterbalancing block-order between-subjects does not cancel out these distortions, we show in study 4 that counterbalancing block-order repeatedly within-subjects can eliminate order effects.