Previous research has correlated lower intellectual ability with suicide. Using population-based registries in Israel, Dr. Mark Weiser of Tel Aviv University and colleagues examined the correlation of IQ with subsequent suicide in men, all of whom have cognitive testing at age 17 by the national draft board. The Israeli hospital registry allows determination of diagnoses in anyone who has inpatient treatment. Causes of death were determined by examining the Israeli vital statistics registry; only unambiguous suicides were included. According to Weiser, this probably underestimated suicides as some proportion of deaths with undetermined cause were likely suicides.
The researchers began with 930,589 consecutively tested men from draft board records but excluded those that had developed psychosis within a year of testing, those hospitalized for non-psychotic illness, and those with missing data, which left a final sample of 596,607 men. Of these, 2881 had been hospitalized subsequently for schizophrenia, and 566,726 men were controls who had had no psychiatric hospitalizations. During the follow-up of 10 years, 319 men in the control group and 25 in the schizophrenia group died by suicide. In men with schizophrenia, those with an IQ one standard deviation or more above the mean had an odds ratio (OR) of suicide of 4.5 (p < 0.001) compared with the reference group of men without schizophrenia and with average IQ. Men with schizophrenia and intelligence one standard deviation below the mean had an OR of suicide of 1.8. Dr. Weis said that 60% of suicides in the schizophrenia group occurred within 6 months of hospital discharge.