Trends in preschool lead exposure, mental retardation, and scholastic achievement: association or causation?

This study shows that 1936-1990 preschool blood lead trends explain 65% of the 1948-2001 variation in USA mental retardation (MR) prevalence, 45% of the 1953-2003 variation in the average scholastic achievement test (SAT) verbal score, and 65% of the 1953-2003 variation in the average SAT math score. These temporal relationships are characterized by best-fit time lags (highest R(2) and t-value for blood lead) consistent with lead-induced cognitive damage in the first year of life: a 12-year lag for school-age MR, and a 17-year lag for SAT scores. Recent shifts in age-specific MR prevalence are consistent with recent trends in preschool blood lead. SAT and MR trends by race are consistent with racial differences in how 1960s slum clearance affected childhood exposure to severe lead paint hazards. SAT trends by Hispanic origin are consistent with an especially sharp fall in preschool blood lead in New York City since 1970.