While empirical economics has made important strides over the past half century, there is a recent attack that threatens the foundations of the empirical approach in economics: external validity. Certain dogmatic arguments are not new, yet in some circles the generalizability question is beyond...

The traditional approach in experimental economics is to use a between-subject design: the analyst places each unit in treatment or control simultaneously and recovers treatment effects via differencing conditional expectations. Within-subject designs represent a significant departure from this...