Rick Nevin
Causation Indicator: Strength

    The strength of the relationship between trends in preschool lead exposure and subsequent trends in mental retardation (MR), Scholastic Achievement Test (SAT) scores, and unwed pregnancy and crime rates is reflected in very high statistical significance of the preschool lead exposure variable in regression (statistical) analyses and in the very high percent of variation in education and behavior trends explained by earlier preschool blood lead trends (regression R-squared). 

    USA MR prevalence (percent of public school students in special education for MR), USA unwed teen pregnancy rates, and international crime rates have varied by several orders of magnitude across decades.

    For MR and SAT scores, USA preschool blood lead trends explain:

  • 65% of the variation in MR prevalence from 1948 through 2001;
  • 45% of variation in the average SAT verbal score from 1953 to 2003; and
  • 65% of the variation in SAT math scores from 1953 to 2003.

    For unwed teen pregnancy, USA abortion legalization and preschool blood lead trends explain:

  • 96% of the 1955-1997 variation in unwed pregnancy rates for ages 15 to 17; and
  • 94% of of the 1955-1997 variation for ages 18 and 19.

    For international crime trends through 2002, preschool blood lead trends explain:

  • 63% to 93% of the variation in index crime rates (violent plus property crimes) in every one of nine nations examined;
  • 91% to 93% of the variation in aggravated assault rates in the USA and Britain;
  • 84% to 90% of the variation in rape rates in the USA and Britain;
  • 70% to 89% of the variation in robbery rates in the USA, Britain, Canada, Australia, West Germany, and New Zealand;
  • 65% to 91% of the variation in burglary rates in the USA, Britain, Canada, Australia, West Germany, and New Zealand, and France. 
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