Results from US NIT experiments in the 1970's overestimated labor supply effects by relying on self-reported estimates.

"The major findings of this paper can be briefly summarized. Estimates computed with interview data collected during the SIME/DIME experiment indicate that husbands, wives, female family heads, and young nonheads who received the experimental treatment on average reduced their earnings and employment by appreciable amounts. Because the experimental treatment also created incentives to misreport earnings and employment status during interviews, however, we argued that the interview-based estimates can seriously overstate true reductions in work effort"