[coldtea]

Yes. Which is why there are also IQ tests for pre-school kids.

Besides the declining groups have the same education with the earlier ones.

[tovej]

All of these effects are explained much better by social factors. If you're poor or discriminated against, you get less nutrition, less education, and face barriers in trying to improve both.

[coldtea]

>If you're poor or discriminated against, you get less nutrition, less education, and face barriers in trying to improve both.

Which doesn't matter, since they measured rich and middle class, and poor and discriminated against both before and after.

Did you think the new measurements were done at some ghetto and the earlier higher ones at Martha's Vineyard?

[tovej]

Could you please elaborate on why measuring the same group somehow eliminates social effects?

Are you claiming social factors have remained constant during the measuring period? Because they very obviously haven't.

If you're aware of the Peter principle, and how inequality compounds over time, then you know that the rate at which social factors change is correlated with their quantile values.