Journal Article
Randomized controlled trials (RCTs) in the social sciences are typically not double-blind, so
participants know they are “treated” and will adjust their behavior accordingly. Such effort
responses complicate the assessment of impact. To gauge the potential magnitude of effort
responses we implement a conventional RCT and double-blind trial in rural Tanzania, and ran-
domly allocate modern and traditional cowpea seed varieties to a sample of farmers. Effort
responses can be quantitatively important—for our case they explain the entire “treatment effect
on the treated” as measured in a conventional economic RCT. Specifically, harvests are the same
for people who know they received the modern seeds and for people who did not know what type
of seeds they got; however, people who knew they had received the traditional seeds did much
worse. Importantly, we also find that most of the behavioral response is unobserved by the analyst,
or at least not readily captured using coarse, standard controls.