[Update: Random Human left a comment which sums up my feelings on this matter:
Yeah, the tests seem to discriminate just fine. This is really troubling data for the racial-hereditarian position and has caused me to update away from it to a degree. It’s obviously not a slam dunk that completely does away with the debate but it’s really troubling data. Even more troubling is the “meh, whatever” reaction from the top hereditarians. Reasonable objections have been raised by the commentators here but no-one has really succeeded in explaining this away.
In response to my recent posts, I’ve received a salvo of tiresome rationalizations. Here’s a typical one:
“On the other hand, it is not necessary to invoke psychometric alteration in order to suggest that GCSE and other testing regimes have been changed in order to (among other imperatives) minimise the apparent statistical gap between negroes and other ethnic groups. The way in which this has been achieved, it would appear to me, is that the tests have been sufficiently dumbed down and made stultifying, that they do little to discriminate amongst the right-hand side of the bell curve and therefore”
One way to evaluate whether the above is true is to look at the variance in scores and the g-loadings of the tests. Alternatively, we can compare the racial differences to class differences. The latter we know are, in part, due to genetically conditioned differences in intelligence. Below are graphs for indexes of cognition by race and class.
So in the LSYPE data, the the highest 1/5th, in SES, scores about 1 SD above the lowest 1/5th. Which is comparable to the difference in the US. The ethnic differences, however, aren’t.
Graph 1 — Goodman et al., 2009. Inequalities in educational outcomes among children aged 3 to 16.
Graph 2 — Goodman et al., 2011. Children’s educational attainment and the aspirations, attitudes and behaviours of parents and children through childhood in the UK