[defrost]

Or, given at least half the US population was non urban | non built up areas for the bulk of the leaded gasoline years, it might something like "half the population lost at least 5 IQ points".

Distributions are often more interesting than averages or medians alone.

[astrange]

IQ points are normally distributed results of IQ tests, so the average is the median and you already know the distribution. I guess they should say how the SD changed though.

Reporting a loss of theoretical IQ points is weird terminology since IQ people want you to believe it's measuring something that exists called "g", but then they don't report this result as a loss of "g". Of course they also happily claim every other test that produces a number like the SAT is also a true measurement of your intelligence and you're doomed to never be able to increase it. Basically they just believe any statement as long as it's got numbers in it and it says something they like.

[defrost]

The geographic distribution of the population affected by lead - it seems clear that car dense populations would be more affected that open sparse rural populations, and so the question of distribution of exposure levels across humans becomes of interest.