According to Phys.org:
Researchers from UCL Anthropology used the lost letter technique to measure altruism across 20 London neighbourhoods by dropping 300 letters on the pavement and recording whether they arrived at their destination. The stamped letters were addressed by hand to a study author’s home address with a gender neutral name, and were dropped face-up and during rain free weekdays.
The results show a strong negative effect of neighbourhood income deprivation on altruistic behaviour, with an average of 87% of letters dropped in the wealthier neighbourhoods being returned compared to only an average 37% return rate in poorer neighbourhoods.
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