- Mediation analysis seeks to understand how or why a predictor (X) influences an outcome (Y) through an intervening variable (M). Interest in mediation has grown significantly since the 1980s. - Early work on mediation was done by Sewall Wright, Ronald Fisher, and Herbert Hyman. In the 1980s, Judd & Kenny, James & Brett, and Baron & Kenny proposed steps for testing mediation that became widely used. - A key development was defining the indirect effect (the product of paths a and b) as the measure of mediation and ways to statistically test it, like the Sobel test. Mediation analysis has since been extended to more complex models. -