Researchers in economics and other disciplines are often interested in the causal effect of a binary treatment on outcomes. Econometric methods used to estimate such effects are divided into one of two strands depending on whether they require the conditional independence assumption (i.e.,...

It is increasingly common in empirical research to merge data sets containing different units of observation. When the units are not nested, a crosswalk specifying how the units from one data source are allocated to the units of the other is needed. Unfortunately, most crosswalks are ad hoc, a...