A meta-analysis of lost-letter field experiments

The lost-letter technique (Milgram et al., 1965) has been used for almost 60 years to measure social attitudes and helping behavior in psychological, sociological, and economic research. We provide a meta-analysis of lost-letter experiments to summarize the evidence. We analyze 78 studies with an overall sample size of 53,504 letters from 18 countries on five continents. We find an average return rate of 50 percent across all countries. Our meta-analysis shows that the return rate is lower for political or deviant issues. Stamped letters are also more likely to be returned, but letters with money are not more likely to be returned. A high socio-economic environment increases the chances of the return. We conclude that in line with the lost-letter paradigm, the technique allows capturing citizens’ attitudes toward the issue communicated. However, citizens do not act selflessly but react differently depending on the type of incentives.