Purpose

The Carroll Human Cognitive Abilities project (C-HCA) was initiated by the Institute for Applied Psychometrics (IAP) in the fall of 2002.  The goal of the C-HCA Project is to build upon the past 60+ years of factor analytic research on the structure of human cognitive abilities (research which was recently summarized and integrated in John B. Carroll’s (1993) seminal Human Cognitive Abilities: A Survey of Factor Analytic Studies) and to extend this line of research into the future.  The primary goals of the project are to:

• Electronically archive and document the 460+ datasets used in Carroll's seminal review so they can be made available for secondary analysis by students and researchers in the area of human cognitive abilities
• Supplement Carroll's 460+ (largely pre-1985) datasets with additional datasets published since the mid-1980's in order to extend and expand the pool of datasets available for analysis regarding the structure of human cognitive abilities.
• Establish a CHC HCA "Work Group" that will develop long-term plans for: (a) retrospective re-analysis of the 460+ datasets analyzed by Carroll with contemporary statistical methods (e.g., confirmatory factor analysis) and (b) prospective analysis of contemporary (post-1985+) datasets
• Produce manuscripts intended to refine and extend the understanding of the nature of the broad and narrow abilities subsumed by the CHC theory of human cognitive abilities.

CHC Theory

The Cattell-Horn-Carroll (CHC) theory of cognitive abilities is widely recognized as the most empirically validated theoretical structural model of human cognitive abilities.  CHC theory has evolved over 100 years of psychometric-based research.  Previously recognized as Gf-Gc theory, the Cattell-Horn Gf-Gc  (Horn, 1991; Horn & Noll, 1997) and Carroll three-stratum models of cognitive abilities (Carroll, 1993, 1997) have recently been integrated under a common theoretical umbrella (viz., Cattell-Horn-Carroll theory).  [Click here for visual-graphic brief summary of evolution of psychometric theories from Spearman's g to contemporary CHC]

CHC theory is a hierarchical framework of human cognitive abilities that consists of three strata: general intelligence or g (stratum III), broad cognitive abilities (stratum II), and narrow cognitive abilities (stratum I). The broad cognitive abilities include Fluid Reasoning (Gf), Comprehension-Knowledge (Gc), Short-term Memory (Gsm), Visual Processing (Gv), Auditory Processing (Ga), Long-term Retrieval (Glr), Processing Speed (Gs), and Decision/Reaction Time or Speed (Gt), Reading and Writing (Grw), and Quantitative Knowledge (Gq; McGrew & Flanagan, 1998). The broad cognitive abilities subsume approximately 70 narrow cognitive abilities. It is important to note that the primary architects of CHC theory do not agree on the validity of g.  Carroll’s model includes a higher-order general intelligence factor while Horn argues against the validity of g.

Carroll's Synthesis

The publication of John B. Carroll’s seminal Human Cognitive Abilities: A Survey of Factor Analytic Studies (Carroll, 1993) provided a much needed systematic organization and integration of over 50 years of research on the structure of human cognitive abilities.  In this treatise, Carroll reported the results of a systematic exploratory factor analysis of over 460 human ability data sets, many of which were classic data sets reported during the past 50 to 60 years.  Through the application of a systematic and uniform methodology, Carroll produced an empirical meta-analysis of the extant human cognitive abilities literature.

Without a doubt, Carroll's factor analytic meta-analysis of the world's literature on human cognitive abilities is the pivotal contribution that has resulted in the recognition of a systematic taxonomic system for organizing and describing human cognitive abilities.  According to Richard Snow (1993):

John Carroll has done a magnificent thing:  He was reviewed and reanalyzed the world’s literature on individual differences in cognitive abilities, collected over most of a century, to reach an integrated picture.  No one else could have done it.  No one else would have applied so consistent and impartial a system on the literature, and reached so balanced, complete, and useful a conclusion.  It is a monumental contribution, destined to be bought and read in every university the world over that has a psychology or education department, and to be on many individual scholars shelf as well.  It defines the taxonomy of cognitive differential psychology for many years to come (comments on back cover of Carroll, 1993).

The Role of IAP

Through a fortuitous sequence of events, Dr. Kevin McGrew, Director of Institute for Applied Psychometrics (IAP) and a Visiting Professor of Educational of Psychology at the University of Minnesota, has possession of the original printouts for all analysis used in Carroll's 1993 work.  Not only do the printouts contain the factor analysis summaries that are available for purchase (on disk) from Cambridge University Press, but they also include:  (a) detailed output of file pre-processing, (b) extended statistical output, (c) many traditional exploratory factor analysis solutions (e.g., principal factor models with orthogonal or oblique rotations) and interpretations that have never been published, (d) hand-written notes by Carroll, and (e) hand plotted scree-plots.  More importantly, the original data used for each analysis (the correlation matrix) was included within the extended factor analysis output for each analysis. As a result, IAP, together with Evans Consulting (Jeffrey Evans) decided that it was important, both from a  historical and research perspective, to preserve and make available the 460+ correlation matrices that served as the basis for the current CHC taxonomy of human cognitive abilities.  This initial project was the impetus for the expanded CHC HCA project