We use data on professional chess tournaments to study how endogenous selection affects the relationship between age and mental productivity in a brain-intensive profession. We show that less talented players are more likely to drop out, and that the age-productivity gradient is heterogeneous by...

We use a natural experiment to show that the presence of an external examiner has both a direct and an indirect negative effect on the performance of monitored classes in standardised educational tests. The direct effect is the difference in the test performance between classes of the same...