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Handedness and intellectual achievement: An even-handed look

https://doi.org/10.1016/j.neuropsychologia.2007.09.009Get rights and content

Abstract

Evidence from a large-scale study of 11-year olds in Britain suggests that ambidextrous individuals may be disadvantaged in tests of verbal, nonverbal, reading, and mathematical skills relative to right- and left-handers, but this basic finding was not replicated in another study of younger boys in Germany. Here, we present data based on a television show in which members of the public were given an IQ test. Some individuals were also asked to state whether they wrote with the left hand, right hand, or either hand. The data support the earlier finding that ambidextrous individuals perform more poorly than left- or right-handers, especially on subscales measuring arithmetic, memory, and reasoning, and extend that finding to adults.

Section snippets

Method

The New Zealand IQ Test was developed by writing 160 items across various dimension, and then administering these to a pilot group along with the Ravens Matrices and parts of the WISC (verbal comprehension, perceptual organization, working memory, and processing speed). Sixty items were chosen to maximize the relations between the total IQ score from the different tests, with six items in each of the following dimensions of intelligence: language ability (meanings, anagrams), numerical ability

Results

IQ was estimated for all 1355 respondents, ranged from 85 to 135, with a mean of 99.6 and a standard deviation of 15.4. The correlation between the New Zealand IQ Test and the total Raven was .67, and with the WAIS was .69. The estimates of reliability exceeded .90. Principal component analysis yielded a single component with an eigenvalue greater than 1.0, and loadings on the component are shown in Table 1. Each subtest therefore contributed approximately equally to a general factor.

Of the

Discussion

Despite the small number of respondents describing themselves as ambidextrous, the results provide support for the finding that there is a dip in intellectual performance among the ambidextrous relative to left- and right-handers (Crow et al., 1998), and also confirm earlier evidence that there is little if any difference between left- and right-handers (Hardyck et al., 1976).

Although the survey was not designed specifically to test for the effects of handedness, a number of considerations

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      In the case of performance measures, some studies use a large number of manual tasks (e.g., Witelson et al., 2006, 12 items) when others use just one to three items (e.g., Calnan and Richardson, 1976). In addition, while in some cases handedness is treated as a continuous variable (e.g., Crow et al., 1998; Nettle, 2003; Resch et al., 1997), in other studies handedness is treated as a categorical variable, with distinct categories based either on a binary (left- and right-handers) or a three-way (or more) handedness classification (left-, mixed- and right-handers) (e.g., Annett and Manning, 1989; Corballis et al., 2008, respectively). Moreover, different cut-off criteria have been used to separate handedness groups.

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