Evidence for a positive ecological correlation of regional intelligence and suicide mortality in the United States during the early 20th century

Several contemporary cross-national and intranational geographic studies have reported positive ecological (group-level) associations of intelligence and suicide mortality. These findings are consistent with facts from suicide research and with an evolutionary view of suicidal behavior. The present research extended these accounts cross-temporally. Analysis of E. L. Thorndike's state-level personal quality scores and standardized birth rates of eminent persons, taken as proxy variables for regional intelligence, along with historical state suicide rates (1913-1924 and 1928-1932) showed that intelligence and suicide mortality across the U.S.A. were already clearly positively related during the early 20th century, suggesting time stability of the effect. Within the U.S.A., the effect is possibly due to state differences in the ethnic composition, which correspond to both suicide rates and intelligence proxies. It is argued that the most parsimonious interpretation of these ecological findings remains that they indeed reflect individual-level effects, that a positive link between intelligence and suicide is entirely compatible with positive overall links between intelligence and health and longevity, and that the ultimate explanative background for the positive link between intelligence and suicide may be provided through the framework of Rushton's differential K theory.