The identification of average causal effects of a treatment in observational studies is typically based either on the unconfoundedness assumption or on the availability of an instrument. When available, instruments may also be used to test for the unconfoundedness assumption (exogeneity of the...

To study effects of out-of-school learning we use data on boarding home pupils who attended elementary public schools in the 1940's. The out-of-school environment at the boarding homes could be considered being more learner friendly than the home environment on average: the pupils at the...

In many cases assignment to a treatment may affect concomitant variables. I show how a concomitant variable can be used to corroborate evidence from an observational study. In the observational study two types of training programs are compared. One program is part of regular Swedish labor market...