Longitudinal designs are needed because the strongest contact effects are least studied.

Evidence

We need research on several points. While the recategorization of the unified group, if attained, appears to yield the maximum in prejudice reduction, we have little data on how this effect generalizes. Further, we must understand how the four contact processes of change are activated and become important at each stage. The thrust of the time dimension is to underline the need for longitudinal research on intergroup contact. Though rare in this literature, this reformulated theory holds that such research designs are necessary for further progress. — Thomas F. Pettigrew, Intergroup Contact Theory, 88

Categorization

• SEED: Article angle — ‘the replication problem in contact research’: the most celebrated outcome (recategorization reducing prejudice) has the thinnest evidence base.
• QUESTION: How well does recategorization-driven prejudice reduction generalize beyond the contact setting, and does it decay over time?