Rick Nevin
Causation Indicator: Dose-Response

    Controlled studies show a dose-response relationship between preschool blood lead and IQ later in life: A loss of 7.4 IQ points due to blood lead of 10 versus 1 mcg/dl, and 15 to 25 IQ points associated with blood lead of 40 to 80 mcg/dl.  Preschool blood lead trends show a corresponding population-dose-response relationship with population MR, SAT scores, crime and unwed pregnancy rates.  Blood lead rose over four-fold from the 1930s through the 1960s and MR prevalence increased by a similar order of magnitude with a 12-year lag.  The fall in MR from the 1970s to 1992 was also roughly proportionate to the earlier decline in preschool blood lead, before the introduction of a new IQ test used in school evaluations in the early-1990s.

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