The Interaction of Ability and Motivation in Performance: An Exploration of the Meaning of Moderators1

It was hypothesized that one possible explanation of moderator effects is that they are due to different degrees of homogeneity with respect to a causal variable among different subgroups. This hypothesis was tested in a laboratory experiment in which performance was predicted from ability using motivation as the moderator. Ability was measured with a work sample and motivation was varied by assigning goals with different degrees of difficulty and specificity. It was found that ability predicted performance better in groups which were homogeneous with respect to motivation that in those which were motivationally heterogeneous. A moderated regression analysis showed that most of the differential validity was reducible to main effects, but significant interaction effects were found. One of them was caused by the fact that in one low motivation condition the variance in performance was reduced, thus decreasing the slope of the regression line.