The Concord Prison Experiment was part of the Harvard Psilocybin Project. It ran from 1961 to 1963 at the Massachusetts Correctional Institution at Concord with volunteers close to parole, and 32 prisoners took part over two years (Doblin, 1998). Leary and five co-authors reported it in 1965 (Leary et al., 1965).
Leary’s early figure compared a 32% return to prison among his subjects with a 56% base rate. Rick Doblin, re-checking records 34 years later, found the two had been measured over different periods: at ten months the base rate was 34.3%, which he called the same as no effect (Doblin, 1998). At two and a half years, 15 of the 21 men whose files he found (71%) had returned, against an expected 56% (Doblin, 1998).
Doblin concluded that the published claims of a treatment effect were erroneous, and that popular histories repeated only the early, favourable figure. He did not conclude psilocybin was useless with prisoners; he argued that one or two sessions without real support after release could not be expected to change much. The study is now a standard example of how uncontrolled figures can mislead.
Sources
- Doblin, 1998, Journal of Psychoactive Drugs
- Leary et al., 1965, Psychotherapy: Theory, Research & Practice
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