Two more tests for a Jensen Effect on c^2

(Note: I think that this analysis is rubbish. Using Falconer’s formula to derive shared environmental estimates is problematic. Generally, ignore it.)

I computed the Jensen Effect on the variance components based on two other studies mentioned in Jensen (1998) on pg. 184. For these studies, only MZT and DZT correlations were recorded, not variance estimates, so I had to use Falconer’s Formula to derive the various coefficients. As for g-loadings, Segal (1985) neither reports these nor reports subtest correlations; as such, I used the Wisc-R US standardization norms reported by Rushton (2003) and by Jensen (1997). I have no idea what Jensen (1998) used. Tambs & Sundet (1984) report rotated factor 1 loadings for their WAIS twin sample; I used those in addition to the US and Italian g-loadings based on the respective national standardization samples as reported by Orsini & Laicardi (2000). Again, I have no idea what Jensen (1998) used.

Segal (1985)

Segal 1985 MZDZ

Segal 1985 Jensen Effect c

Tambs & Sundet (1984)

Tambs et al 1994 MZDZ

Tambs and Sudet (1984) Jensen Effect c

In both of these samples, there were negative correlations between c^2 and g-loadings, a finding which contrasts with the results from the previous three samples. Given the unexpected heterogeneity of results, the best approach moving forward will be to weight results by number of sibling pairs or when so reported mean number of the range of pairs used. This is done below. Now the average Jensen Effect on c^2 is close to zero, which still is significantly different from the average Jensen effect on e^2.

Jensen Effect on c^2 summary2


Jensen, A. R. (1997). Adoption data and two g-related hypotheses. Intelligence, 25(1), 1-6.

Rushton, J. P. (2003). Race Differences in g and the “Jensen Effect”. The scientific study of general intelligence: Tribute to Arthur R. Jensen, 147-186.

Segal, N. L. (1985). Monozygotic and dizygotic twins: A comparative analysis of mental ability profiles. Child Development, 1051-1058.

Tambs, K., & Sundet, J. M. (1984). Heritability analysis of the WAIS subtests. A study of twins. Intelligence, 8(4), 283-293.

Orsini, A., & Laicardi, C. (2000). Factor structure of the Italian version of the WAIS-R compared with the American standardization. Perceptual and motor skills, 90(3c), 1091-1100.

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