The experimentalist looks within: toward an understanding of within-subject experimental designs

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 sample means. Within-subject (WS) designs represent a significant departure from this method, as the same unit is observed in both treatment and control conditions sequentially. While many might consider the choice straightforward (always opt for a between-subject design), given the distinct benefits of WS designs, the author argues that researchers should meticulously weigh the advantages and disadvantages of each design type. In doing so, the author proposes a categorization for WS designs based on the plausibility of recovering an internally valid estimate. In one instance, which the author denotes as stealth designs, the analyst should unequivocally choose a WS design rather than a between-subject design.