Who took the "x" out of expectancy-value theory? A psychological mystery, a substantive-methodological synergy, and a cross-national generalization.

Expectancy-value theory (EVT) is a dominant theory of human motivation. Historically, the Expectancy × Value interaction, in which motivation is high only if both expectancy and value are high, was central to EVT. However, the Expectancy × Value interaction mysteriously disappeared from published research more than 25 years ago. Using large representative samples of 15-year-olds (N = 398,750) from 57 diverse countries, we attempted to solve this mystery by testing Expectancy × Value interactions using latent-variable models with interactions. Expectancy (science self-concept), value (enjoyment of science), and the Expectancy × Value interaction all had statistically significant positive effects on both engagement in science activities and intentions of pursuing scientific careers; these results were similar for the total sample and for nearly all of the 57 countries considered separately. This study, apparently the strongest cross-national test of EVT ever undertaken, supports the generalizability of EVT predictions--including the "lost" Expectancy × Value interaction.