Heterogeneous Effects

[This Guest Blog is a repost of a blog by Markus Eberhardt, published at Vox – CEPR Policy Portal] Recent evidence suggests that a country switching to democracy achieves about 20% higher per capita GDP over subsequent decades. This column demonstrates the sensitivity of these findings to sample selection and presents an implementation which generalises the empirical approach.

An oft-overlooked detail in the significance debate is the challenge of calculating correct p-values and confidence intervals, the favored statistics of the two sides. Standard methods rely on assumptions about how the data were generated and can be way off when the assumptions don’t hold. Papers on heterogenous effect sizes by Kenny and Judd and McShane and Böckenholt present a compelling scenario where the standard calculations are highly optimistic.