Abstract
A recent study by Russell did not duplicate Halstead's factors of biological intelligence. As an approach to understanding this finding, Hal-stead's original correlation matrix was subjected to the same orthogonal principal components analysis used in Russell's study as well as an orthogonal and an oblique factor analysis using communalities. All of Halstead's factors appeared in these analyses. The failure to duplicate Halstead's work was evidently not due to use of different factoring methods. In a second analysis which reduced the number of Halstead's variables to the number used by Russell, one of Halstead's factors (P) did not appear. This factor represented tests measuring the visual threshold, and so it appears to be primarily a perceptual factor.
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