Field experiments and public policy: festina lente

The current state of the art in field experiments does not give me any confidence that we should be assuming that we have anything worth scaling, assuming we really care about the expected welfare of those about to receive the instant intervention. At the very least, we should be honest and explicit about the need for strong priors about the welfare effects of changes in averages of observables to warrant scaling. What we need is a healthy dose of theory and the implied econometrics.