October 08, 2006

Jensen's default hypothesis rejected

A new article in Intelligence presents strong evidence against Jensen's default hypothesis that "group differences in IQ have the same genetic and environmental bases, in the same ratio, that underlie individual differences within a racial group." According to the authors, IQ scores are due both to intelligence, but also to the provisioning of information. Whites and Blacks do not differ in intelligence, but rather in the information that they have acquired. Whites and Blacks are able to answer questions correctness at the same rate when they both possess the same information: this indicates that their brains' processing efficiency is not worse than Whites'. It is in the test items for which Blacks do not possess the same information as Whites that they underperform. Moreover, Whites and Blacks both have the same ability to acquire new information, so it is rather a lack of stimulation rather than lack of any skill of acquiring new information that is the root of Black underperformance. From the paper:
In what ways are African-Americans deprived of access to information? Differences in exposure to information on the parts of African-Americans and Whites are an empirical fact. As noted by Fagan (2000), Hart and Risley (1995) conducted a longitudinal study on the frequency of verbal stimulation and the resulting language development of children from 1 to 3 years of age. They found that amount of exposure to language predicted the vocabulary development and the IQ scores of the children at three years. They also found that the children of professionals (typically, Whites) were exposed to five times the amount of words than were children of parents on welfare (typically, African-Americans). The Hart and Risley results tell us that the child's exposure to words in their homes during their first few years influences their later IQ. Whites and African-Americans differ in IQ by as early as 3 years (Montie and Fagan, 1988 and Peoples et al., 1995). Numerous studies (e.g. see reviews by Bjorklund, 2005 and Courage and Howe, 2002) have focused on the knowledge gained by infants through the infants' ability to process information and how that processing ability during the first year of life is predictive of later IQ (Fagan, 1992). All of these findings tell us that the search for racial differences in the kind of knowledge required to solve items on conventional IQ tests must begin in the first months and years of life.
Intelligence (online early)

Joseph F. Fagan, and Cynthia R. Holland


African-Americans and Whites were asked to solve problems typical of those administered on standard tests of intelligence. Half of the problems were solvable on the basis of information generally available to either race and/or on the basis of information newly learned. Such knowledge did not vary with race. Other problems were only solvable on the basis of specific previous knowledge, knowledge such as that tested on conventional IQ tests. Such specific knowledge did vary with race and was shown to be subject to test bias. Differences in knowledge within a race and differences in knowledge between races were found to have different determinants. Race was unrelated to the g factor. Cultural differences in the provision of information account for racial differences in IQ.


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