Wednesday, September 27, 2006

CHC-based analysis of Spearman's law of diminishing returns in KABC-II

Kudos to one of the best quantoids in school/educational psychology (Dr. Tim Keith), and a serious quantoid in the making (Keith's doctoral student, Mathew Reynolds) re: their "in press" article in Intelligence.
  • Reynolds, M. & Keith, T. (2006, in press). Spearman's law of diminishing returns in hierarchical models of intelligence for children and adolescents, Intelligence (click here to view)
Using CFA methods, Reynolds and Keith investigated Spearman's law of diminishing returns (SLODR) in the norm sample for the CHC-based KABC-II. I'm excited about this paper due to the elegant use of CFA to evaluate whether SLODR exists, and, if it does, at what level of the CHC taxonomy (stratum I, II, or III - with five broad CHC abilities being represented--Gf,Gc,Gv,Glr,Gsm). The abstract provides a sufficient I won't waste any bandwidth.


  • Spearman's “law of diminishing returns” or SLODR refers to a decrease in g saturation as ability level increases. SLODR has been demonstrated in a number of intellectual batteries but several important aspects of the phenomenon are not yet well understood. We investigated the presence of SLODR in the Kaufman Assessment Battery for Children—Second Edition (KABCII), a popular measure of intelligence for children. We used confirmatory factor analysis to investigate the invariance of two hierarchical factor structures across ability groups; the subtest variance explained by the ability factors across groups; and whether SLODR was produced only by subtests with low loadings on the general ability factor. We found that SLODR was present in the KABC-II, and its presence was not dependent on the hierarchical model of intelligence. Moreover, our findings suggest that SLODR acts on g and not on the broad abilities, although the contribution of g to various broad abilities is lower in the high ability group. Finally, SLODR was not produced by the subtests with the lowest g loadings on the general factor.
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