The purpose of this article is to describe statistical procedures to assess how prevention and
intervention programs achieve their effects. The analyses require the measurement of intervening
or mediating variables hypothesized to represent the causal mechanism by which the prevention
program achieves its effects. Methods to estimate mediation are illustrated in the evaluation of
a health promotion program designed to reduce dietary cholesterol and a school-based drug
prevention program. The methods are relatively easy to apply and the information gained from
such analyses should add to our understanding of prevention.
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