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.