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...

We examine empirically the generalizability of internally valid micro estimates of causal effects in a fixed population over time when that population is subject to aggregate shocks. Using panel data we show that the returns to investments in agriculture in India and Ghana, small and medium...