We examine the generalizability of internally valid estimates of causal effects in a fixed population over time when that population is subject to aggregate shocks. This temporal external validity is shown to depend upon the distribution of the aggregate shocks and the interaction between these...

This paper seeks to explain the U-shaped relationship between farm productivity and farm scale - the initial fall in productivity as farm size increases from its lowest levels and the continuous upward trajectory as scale increases after a threshold - observed across the world and in low-income...