[newer update: I guess I goofed with the original analysis. The data file was really difficult to handle and I had to compute a number of values. Somehow I didn’t properly exclude non-score SAT/ACT values (e.g. “enter 999 if you don’t know your score”). Anyways, I reran correlations after recomputing and found a -0.11 correlation between color (going from light to dark this time) and ACT/SAT in the total sample (n=766). When I excluded Blacks whose parents were not born in the US, the (weighted) correlation shot up to – 0.18 (n=552)
So using just the native sample, the n-weighted correlation summed across studies stands at 0.15 (N=4246).
JL, apt as ever, has proposed that the low correlation could be due to selection. Imagine if you selected Blacks and Whites for an IQ of 130. In that subpopulation, racial characteristics would, necessarily, be uncorrelated with IQ even though they are in the unselected population. Similarly, if you selected more and less admixed Blacks for an IQ of 130, racial admixture would, likewise, be uncorrelated (or less correlated) with IQ. Where there IQ differences and selection, one would, nonetheless, find something.. Namely, disproportionalities. As there would be proportionately fewer Blacks than Whites in the former case, in the latter there would be proportionately fewer less admixed Blacks than more admixed Blacks. This brings to mind that rather dated study, Witty and Jenkins (1936), that I once discussed.
To tests JL’s proposal, I compared The NLSF (native) Black sample and the ADDHealth Black national sample in terms of scores and two indices of admixture. To save myself some effort, I used Massey et al. (2007) as a reference for the NLSF data.
1. Nationally, Blacks (born of native parents) score about 850 on V+M SATs (SD= about 200). In the NLSF study, they scored, on average, 1193 circa 1998. So they were, in this sample, maybe 1.75 SD above the population mean. Being 1.75 SD above the national mean, we would expect the NLSF cohort to be at least 1.75 SD x 0.15 above the color mean if the IQ color correlation is around 0.15.
In the ADD health data, the mean color score was 2.34 (SD = 1.06) on a 1-5 scale running from black to white. In the NLSF, the mean score was 4.79 on a 0-10 scale running from white to black (In a figure, Massey et al. describes the scale as 1-10, but the “NATIONAL LONGITUDINAL SURVEY OF FRESHMEN PUBLIC RELEASE CODING MANUAL” indicates that it was a 0-10 scale.) Using the metrics of the Add Health data, Blacks in the NLSF have an equivalent color score of 2.85 or are 0.45 SD more light colored, which coheres with our expectation:
a. Convert the score from the 11 point scale to a score on a 10 point scale going from white to black ( 4.79 x (10/11) = 4.35)
b. Reverse scale to a black to white scale (10-=4.35 = 5.65) and reduce by ½ to a 5 point scale (5.65/2=2.825)
c. Convert to STDV (2.825-2.34)/1.06 =.45 SD)
d. Compare with expectation
3. Likewise with color, we would expect the NLSF cohort to be somewhat more admixed. Being 1.75 SD above the national mean, we would expect the NLSF cohort to be at least 1.75 SD x (some predicted IQ-ancestry correlation — I’ve estimated this to be 0.25) above the national admixture mean, if the IQ white ancestry correlation was (some predicted IQ-ancestry correlation).
In the NLSF study, going by the data in Massey et alia, 16% of the native black group reported being mixed race (i.e. having one black and typically one white parent). In the ADD health data, according to Rowe (2002), out of a Black sample of 4271:
“127 adolescents were self-identified as inter-racial children because they had selected both the White and Black self-descriptors. Of these individuals, 102 were classified as Black by the interviewer. Parental reports were also used to identify possible inter-racial children. The head of household (usually the mother) reported her own race and that of her current spouse or partner. When one parent was reported as Black and the other as White and both lived in the household, the child was classified as interracial. Of 442 interracial children, 56 were classified by the interviewer as Black.”
This gives us a mixed race percent ranging from 3-10 percent. Using the midpoint as our estimate, the ratio of mixed to not is 0.07; and the ratio in the NLSF is .18. Which means that the NLSF cohort is .55 SD more admixed, which coheres with our expectation. (The NLSF cohort was born around 1981 and the inter-racial marriage rate was about 5% then, so this would likely be an underestimation of the NLSF mixed race overrepresentation – if that makes sense).
So, the data coheres with JL’s proposal.]
I suppose I should be commenting on the death of Kim Jong Il or something but…
I checked the test score – color correlation in the National Longitudinal Study of Freshman (NLSF). This was a fairly recent study of individuals at selective colleges. For self-identifying blacks with native born parents, the correlation between self reported SAT/ACT scores and interviewer assessed color was a very low = -0.034 (n= 658) (SATV= -.005; SATM= -.038; ACTC= -.069). This data point is questionable as self report has been found to be unreliable when it comes to scores, particularly when self-reporters have objectively assessed low scores. If we accept this data point, though, the n-weighted correlation stands at -0.13 (n= 4352). [REFER ABOVE.]