The standard deviation of an IQ test is 15 - 16 points across all test takers. That goes up only 1 or 2 points depending on social economc status.
If you double the test length or give up triple test over days, it only goes to 13-15. This is true of student evaluations in the general case.
Exposure to leaded gasoline was dependant on social economic status, gender or profession. Gross Economic status increased remarkably over the time period that Leaded Gas was phased out. Any number created is within alot of other unknows.
Could be true, had been mostly addressed, and other human brain development factors have widely eclipsed the effects of lead in gasoline and in paint chips and dust.
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