The trees and the forest: Investigating variability surrounding an aggregate result

We agree with Arocha that the common and exclusive focus on aggregate results of psychological studies creates problems. While a paradigm shift toward idiographic approaches or control theory might help, we argue that traditional approaches can accomplish more if measures of variability are taken seriously. We discuss three kinds of studies: within-person treatment studies, questionnaire-based studies, and replication studies. For each of these, we suggest ways to improve psychological meaningfulness by investigating variability surrounding aggregate results, without ending up in an either–or choice between aggregate results and separate, individual results.