Peer Review

Commonly used between-subject experimental designs focus on average treatment effects at the group level. One limitation of doing so is that it overlooks the possibility that a minority of individuals may not show any effects, or may even show effects in a direction opposite from the majority. Given it is impossible to identify all moderators of an effect a priori, how do we know for whom and when an experimental manipulation works, has no effect, or backfires? This article describes a theoretical framework (the Cognitive Affective Processing System, or CAPS model) and a study approach (a Highly Repeated Within-Person, or HRWP design) that are capable of assessing whether an experimental manipulation is effective for a given individual, and the psychologically active ingredients of a manipulation that a given person may be most responsive to. In a study on the effectiveness of anti-smoking ads, we identified a feature of ads that did not have an effect on the sample as a whole, but did have statistically significant positive effects on some people, and statistically significant negative effects on some others. The results have implications for work using between-subject research designs and demonstrates how researchers can identify for whom a manipulation may be most effective or ineffective. Social and Personality Psychology Compass Social and Personality Psychology Compass