(Edit: Corrections were made to this.)
In his post, Science for fun and profit, Steve Sailer notes:
“One thing that’s interesting is how seldom these kind of data-mined false positives are published regarding The Gap, despite the huge incentives for somebody to come up with something reassuring about The Gap.”
What you get at times instead of false positives are negatives that are reported as if they were positives. For example, below are the results from the two published, and not infrequently cited, transracial adoption studies in the US concerning Blacks and Whites, Moore (1986) and the MTRAS, with statistical differences noted. (I calculated d’s using the means and standard deviations presented in the original papers.)
Column F gives the Cohen’s d found between the adopted groups (e.g., Blacks and mixed race kids). Column G gives the significance levels based on Welche’s unpaired t, 2-tail, 0.05. Column H gives the Cohen’s d predicted by a genetic hypothesis with genetic d =1 and a heritability of 0.4 in childhood and 0.6 in adolescence (i.e., 1 x SQRT(.4) and 1 x SQRT(.6)). Column I gives the Cohen’s d predicted by a genetic hypothesis for WGH = 0.5. Column J gives the Cohen’s d between the found results and the genetic prediction in H (i.e., H-F). Column K gives the Cohen’s d between the found results and the genetic prediction in I (i.e., I-F). Column L gives the significance of J (again using Welche’s unpaired t). Column M gives the significance of K (again using Welche’s unpaired t).
…. Sure the Moore (1986) results which are lauded as proof of racial environmental determinism weren’t significantly different from zero, but they also weren’t significantly different from a genetic hypothesis’s predictions (genetic d =1). (And using one tail tests while increased the WGH to 0.5 didn’t remedy the lack of significant effects.)
But no one mentions the latter point. Richard Nibett, for example, in his 2007 NYtimes op-ed, misleadingly informs us:
“A superior adoption study — and one not discussed by the hereditarians — was carried out at Arizona State University by the psychologist Elsie Moore, who looked at black and mixed-race children adopted by middle-class families, either black or white, and found no difference in I.Q. between the black and mixed-race children. (All Brains Are the Same Color)”
For comparison the MTRAS — the inferior adoption study which had the deficiencies of being longitudinal, of including multiple indexes of cognitive ability, of including mixed and full race individuals along with adopted and non adopted whites, and of having authors which estimated the heritabilities of IQ in the sample — gives us six adopted estimates: Mixed-Black time 1, time 2 -White-Black time 1, time 2 – White-mixed time 1, time 2. Of then, 5 are significantly different from zero and only 1 is significantly different from the predictions of a genetic hypothesis. (Using one tail tests and setting the WGH to 0.5 for both time 1 and time 2 we get 5 values significantly different from zero and 2 values which are significantly greater than predicted by a genetic hypothesis).
(It follows from the above that, as I noted elsewhere, results from adoption studies — all two of them –provide more evidence for a genetic hypothesis than for a shared environmental hypothesis — no matter how you slice and dice the results. It’s interesting (to me) that no one has bothered to make this point, statistically.)
Now, this is merely one example of misleadingly reported negatives. Others, just from Nisbett’s All Brains Are the Same Color piece, include Nisbett’s discussion of the famed Scarr et al. (1977) study and his discussion of the Witty and Jenkins (1936) study .
So, ya, when it comes to the GAP you won’t get a lot of false positives. But not infrequently you will get falsely reported negatives.
Scarr et al., 1992. IQ Correlations in Transracial Adoptive Families
Weinberg et al., 1992. The Minnesota transracial adoption study: A follow-up of IQ test performance at adolescence. Tabel 2.