“Mixed achievement”

In the IQ wars, Environmentalists (e.g., Nisbett and Flynn) make much out of a few studies which show little or no significant difference between biracials and Whites. Others (e.g., Murray and Rushton) point to studies which show their hypothesis’ predicted gap and contend that the biracial data largely supports a genetic interpretation. The studies present a conflicting picture and it’s difficult to adjudicate between the environmentalist and hereditarian claims because the subject numbers are rather small. One way to approach such situations is by conducting a meta-analysis. To that end, I did a literature search and located 6 studies that contain data on the IQs of American biracials. I then computed Cohen’s d for Biracial-Whites and Biracial-Blacks across studies and found respective d’s of 0.29 (N= 577) and 0.49 (N= 431).

Scarr et al. (1994)…..55…..0.66
Willerman et al. (1974).129…..0.3
Eyferth (1961)……….177….0.05
Harrison et al. (2001)..128….0.32
Gullickson (2004)……..88…..0.46

Study……………… .N……..d
Scarr et al. (1994)……55…….0.55
Willerman et al. (1974)..129……0.55
Harrison et al. (2001)…128……0.51
Gullickson (2004)………88…….0.49
Moore (1986)…………..31…….0.1

I then estimated the between group heritability. This was done by determining the cross sample average deviation from the genetic prediction that Biracials will perform halfway between the parental populations and then subtracting this from one. So, for example, Scarr et al. deviated 3% from a genetic prediction while Eyferth deviated 93%. The assumption here is that genetic factors condition intermediate performance while environmental factors tend to make biracial individuals more similar to one or the other of their parental populations, situation depending. The more heterogeneous the scores across samples the more environmental influence. Based on this assumption, I estimated a heritability of 0.43. The correlation between age and deviation from a genetic prediction was -0.55, which indicated that older samples tend to conform closer to a genetic prediction than younger ones, which is consistent with a genetic hypothesis. The studies used and the scores are listed below.

These results were corroborated by data on biracial GPA, rates of school attendance, and other indexes of cognitive performance. Overall, the data is not inconsistent with a genetic hypothesis.

Fairlie, 2009. Can the “one-drop rule” tell us anything about racial discrimination? New evidence from multiple race question on the 2000 Census.

Analysis of 2000 census data. Biacial BW fall intermediate to Whites and Blacks in the numbers of years of schooling and percent of college degrees but earn slightly less than Blacks.

Kao, 1999. Racial identity and Academic Performance: An Examination of Birracial Asian and African Youth

Analysis of National educational longitudinal survey. Biracial BW have a slight statistically non-significant advantage over Blacks and a significant disadvantage to Whites in math scores, grades, and rates of retention

Fryer et al., 2008. The plight of mixed race adolescents

Analysis of ADD Health data. Biracial BW students have GPAs that are intermediate to Black and Whites

Herman, 2009. The Black-White-Other achievement gap: Testing theories of academic performance among multiracial and monoracial adolescents

Analysis of School data in California and Wisconsin. Biracial BW students have GPAs that are intermediate to Blacks and Whites


Eyferth, 1969. Eine Untersuchung der Neger-Mischlingskinder in Westdeutschland

Data Source: German-American Children fathered by US Soldiers
IQ test: WISC
Notes: Did not have standard deviations, assumed SD= 15

Normed scores (Flynn corrected as reported in Lynn 2006)
Black….(set at White minus 15)

Gullickson, 2004. Amalgamations, New and Old: The Stratification of America’s Mixed Black/White Population
Data Source: National Longitudinal Survey of Youth 97

Normed scores:

Harris and Thomas, 2002. The educational cost of being Multiracial: evidence from a National survey of Adolescence

Data Source: Longitudinal Survey of Adolescent Health (Add Health).
IQ test: Picture Vocabulary Test (AHPVT)
Notes: This same data set has been analyzed by Rowe (2005); N and d depend on inclusion criteria.

Normed scores:
Harrison et al. (2002)

Moore, 1986. Family socialization and the IQ test performance of traditionally and transracially adopted black children

Data Source: Adoption Study
IQ test: WISC

Moore (1986) (Flynn corrected as reported in Loehlin 2000, SD adjusted)

White……(set at Black plus 15)

Scarr et al., 1992. The Minnesota Transracial Adoption Study: A Follow-Up of IQ Test Performance at Adolescence.

Data Source: Adoption Study

Scarr et al. (1994) (Flynn corrected as reported in Loehlin 2000)

Willerman et al., 1974. Intellectual development of children from interracial matings: Performance in infancy and at 4 years

Data Source: Longitudinal Collaborative Study
IQ Test: Stanford-Binet

Normed scores:
Willerman et al. (1974)

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3 Responses to “Mixed achievement”

  1. Statsquatch says:

    Interesting, do you mean .58? What is SD, Cohen’s D or the standard deviation? Also, it is better to weight with SD than sample size.

  2. Chuck says:

    Thanks for catching the .58. As for “SD,” I meant “d” or standardized mean difference; I guess “SD” is a bit confusing — If I get a chance, I’ll change it. As for the computation, I just weighted the ds. The effort intensive part was doing a lit review to make sure I hadn’t missed any studies. It’s amazing that that’s all there was. Apparently, though, the next NAEP is going to allows for multiracial classifications, so that will open a large data source.


  3. Pingback: Color Differences: Corrections and Further Analysis. Part 2 | Human Varieties

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