Unfortunately, the books also indulge another sort of irrationality: the demand for big, general statements even if you’re discussing limited, context-specific matters. The authors criticize over-promising and generalizing in the aid business, but they too often do their own exaggerating when it comes to what their methods can deliver. Both books end with overselling, “five key lessons” (Banerjee and Duflo) or “seven ideas that work” (Karlan and Appel), ignoring their own previous cautions about sensitivity to context and the limits to each intervention. Other economists criticize overselling as a common fault of those who do these small experiments.
But let’s extend the same consideration to these authors that they show for the people they study. They have fought to establish a beachhead of honesty and rigor about evidence, evaluation and complexity in an aid world that would prefer to stick to glossy brochures and celebrity photo-ops. For this they deserve to be congratulated—and to be read.