150 stamped and 150 unstamped letters were “lost.” Three different addresses, designed to indicate different degrees of apparent importance, were used. The return rate for stamped letters was significantly higher than the return rate for unstamped letters. The apparent importance of the letter did not have a significant effect upon return rate.
SimonW.GillenM.Return rates of “lost letters” as a function of whether the letter is stamped and amount of money apparently in the letter. Psychological Reports, 1971, 29, 141–142.
