Predicting what will happen when we act. What counts for warrant?

Area of Science:

• Policy analysis
• Evidence-based research
• Social science methodology

Background:

• The reliance on randomized controlled trials (RCTs) for evidence-based policy is widespread.
• A critical gap exists in understanding how RCT findings translate to different contexts.
• The extrapolation of trial results to novel policy implementations is often assumed but rarely justified.

Purpose of the Study:

• To evaluate the extent to which randomized controlled trial results inform predictions of policy intervention effectiveness.
• To critically examine the assumptions underlying the generalization of RCT findings.
• To highlight the limitations of RCTs in predicting real-world policy outcomes.

Main Methods:

• Conceptual analysis of evidence-based policy arguments.
• Examination of the inferential leaps from localized trial results to broader policy predictions.
• Review of the premises required for generalizing RCT findings.

Main Results:

• Arguments for policy effectiveness based on RCTs rely on numerous premises not supported by the trials themselves.
• RCTs provide only indirect evidence regarding the effectiveness of interventions in new settings.
• The justification for generalizing RCT results is often weak, relying on unverified assumptions.

Conclusions:

• Randomized controlled trials alone are insufficient for reliably predicting the effectiveness of policy interventions in different contexts.
• Making accurate predictions about policy effectiveness requires integrating evidence beyond RCTs, including contextual factors and theoretical assumptions.
• A more nuanced approach is needed to bridge the gap between trial findings and practical policy implementation.