Rick Nevin
Causation Indicator: Consistency

    MR, SAT, crime, and unwed pregnancy trends show a consistent association with 1936-1990 USA blood lead trends, encompassing changes in a large, diverse, national population across four time zones and over five decades.  Declining MR from 1939-1947, tracking earlier declines in lead paint, shows the same association back to 1920s birth years.  Crime trends show the same consistent relationship in Canada, Britain, Finland, France, West Germany, Italy, Australia, and New Zealand.   

    These trends are consistent with controlled studies showing a causal association between lead poisoning and MR in individual children. The negative correlation between blood lead and SAT trends is consistent with extensive research demonstrating an inverse relationship between preschool blood lead and IQ, and research showing IQ is an excellent predictor of academic achievement.  The long-term nationwide association between blood lead, MR, and SAT trends is consistent with slum clearance trends and subsequent racial trends in MR and in SAT scores, and with large Puerto Rican SAT gains after a large fall in New York City preschool blood lead.

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