Successfully scaled solutions need not be homogenous

Al-Ubaydli et al. point out that many research findings experience a reduction in magnitude of treatment effects when scaled, and they make a number of proposals to improve the scalability of pilot project findings. While we agree that scalability is important for policy relevance, we argue that non-scalability does not always render a research finding useless in practice. Three practices ensuring (1) that the intervention is appropriate for the context; (2) that heterogeneity in treatment effects are understood; and (3) that the temptation to try multiple interventions simultaneously is avoided can allow us to customize successful policy prescriptions to specific real-world settings.