© Hodder Education 2010 Part 6 Individual Differences Chapter 41 Intelligence

© Hodder Education 2010 Theories of intelligence (1) Psychometric (factor-analytic) theories Spearman’s (1904, 1967) two-factor theory: individual differences largely attributable to differences in their general intelligence factor (g). Burt (1949, 1955) and Vernon’s (1950) hierarchical model: a number of group factors lie between g and specific intelligence factors (s). Thurstone’s (1935, 1938, 1947) primary mental abilities (PMAs): spatial (S); perceptual speed (P); numerical reasoning (N); verbal meaning (V); word fluency (W); memory (M); inductive reasoning (I). Guilford’s (1959) structure of intellect model: content x operations x products  150 distinct mental abilities.

© Hodder Education 2010 Theories of intelligence (2) Fluid (gf) and crystallised (gc) intelligence (Horn & Cattell, 1967, 1982): gf = relatively free of cultural influences; gc = based on knowledge acquired from schooling/other life experiences. The information-processing approach (e.g. Sternberg, 1979, 1987): g results from the operation of (mainly) metacomponents (i.e. higher-order control processes used in planning how to solve a problem, choosing between alternative courses of action, monitoring one’s progress, etc. Theory of multiple intelligences (Gardner, 1983, 1998): linguistic; logical-mathematical; spatial; musical; bodily- kinaesthetic; interpersonal; intrapersonal; naturalistic.

© Hodder Education 2010 Intelligence testing Individual tests of intelligence are used mainly as diagnostic tests in clinical settings; group tests are used mainly for educational selection and research. Although all tests now use a deviation IQ, standard deviations can still differ between tests. While intelligence = a psychological concept, IQ = a statistical concept: we cannot equate the two. Both the Stanford-Binet and Wechsler scales were originally standardised on whites only; the restandardisation of the former so as to equate the mean scores of women and men illustrates the ideological significance of IQ. This adjustment changes the test’s predictive validity (or efficiency).

© Hodder Education 2010 Explaining individual differences Although several studies show high stability coefficients for IQ, these obscure sometimes very large individual differences. As people’s genetic similarity increases, generally so does the similarity of their environments. This can be overcome by comparing the IQs of monozygotic twins (MZs) reared together (MZsRT) with those raised apart (MZsRA). MZsRA are still more alike than same-sex DZs reared together, suggesting a strong genetic influence. But studies of MZsRA have been criticised on several fundamental methodological grounds. While adoption studies overcome some of these problems, they face problems of their own (e.g. the ‘restrictive variance’ of adoptive families: Kamin, 1981).

© Hodder Education 2010 Heritability & the race and IQ debate ‘Heritability’ is a much misunderstood/misguided concept; calculation of a heritability estimate is based on the assumption that there is no gene–environment interaction (Joseph, 2003). One assumption involved in the hereditarian fallacy (Gould, 1981) = heritability estimates based on within-group differences (such as found in twin studies) can be applied to between-group differences (such as between blacks and whites) (Lewontin, 1976). IQ tests are culturally biased (Segall et al.,1999), and they ‘remain a useful tool for racist ideologues’ (Sweet, 2004).