Early 20th century social ecology of US state IQ and suicide rates: Evidence from the army alpha and beta intelligence test data of Yerkes (1921)

Consistent with a number of facts from suicide research and an evolutionary view of suicidal behavior, positive ecological (group-level) correlations between contemporary suicide rates and intelligence level have been observed in several geographical (cross-national and within-nation) studies (e.g., Lester, 1993, 1995, 2003; Voracek, 2004, 2005a, 2005b, 2006a-h, 2007). The present research extended these accounts cross-temporally to a test of the social ecology of U.S. state IQ and suicide rates during the early 20th century. Analysis of historical state suicide rates (1913-24), along with validated state IQ figures derived from the Army Alpha and Beta Intelligence Test data of Yerkes (1921), showed a clear positive correlation of state IQ with suicide rates (independent of state wealth) across the USA, thus suggesting temporal stability of the effect.