> If all of the IQs in a county went down we might investigate that. There's one.

The average is always by definition exactly 100, neither higher nor lower.

Also, this data already exists. The folks who make standardized tests collect it to use for translating raw results to standardized scores.

> If we were looking for smart people for a role in whatever. There's another.

This is illegal. There are ways to get the same result that are not illegal, and are actively used.

> If we were rating schools. There's a third.

Schooling doesn't do much to iq.

> > If all of the IQs in a county went down we might investigate that. There's one.

> The average is always by definition exactly 100, neither higher nor lower.

The average for the population that the test is normalized is exactly 100. GP was suggesting that if the averaged dropped in a single locality (specifically county, but I'm generalizing), which is completely possible.