Abstract
MANY years of mental testing have shown that most kinds of intelligence are positively correlated, so that a person talented in one direction is more likely than not to be talented in others. This suggests that each ability may be analysed into the sum of parts or ‘factors’, one of which (Spearman's ‘general factor’ 9) is common to every kind of ability. At first, attention was directed mainly to certain dissimilar mental tests which satisfied the tetrad equations. The score of each such test can be expressed as the sum of two parts, which are positive multiples of g and of a ‘specific factor’, uncorrelated with g or with the specific factors occurring in the other tests. This simple form of ‘two-factor theory’ applies to the Spearman-Stephenson form perception tests. But W. Stephenson has shown that the ordinary verbal mental tests have a verbal group factor, and so are analysed into three parts, positive multiples of g, v, and specific factors. However, those who use tetrads are still called ‘the two-factor school’, as opposed to those who prefer other methods (‘the multiple factor school’), such as H. Hotelling and L. L. Thurstone; but there is now no difference in principle or in the final results, merely in technique. It should be remarked that the verbal factor does not itself measure verbal ability, but (roughly) what is left of that ability when the parts due to g and the specific factor are deducted.
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References
J. Gen. Psych., 11, 126; 1934.
” Intelligence, Concrete and Abstract” (Brit. J. Psychol. Monograph Supplement 19), Camb. Univ. Press, 1935. 12s. 6d.
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PIAGGIO, H. Analysis of Intelligence. Nature 137, 39 (1936). https://doi.org/10.1038/137039a0
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DOI: https://doi.org/10.1038/137039a0