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 show how financial and managerial constraints impede experimentation and thus limit learning about the profitability of investments. Imperfect information about one's own type, but willingness to experiment to learn one's type, leads to short-run negative expected returns to investments, with...