2.3 C. CHC (Gf-Gc) Investigations, Integrations, and Extensions
The CIA book
The collective influence of the Cattell-Horn Gf-Gc theory, Carroll’s (1993) treatise, and the publication of the Cattell-Horn Gf-Gc based WJ-R was reflected by nine chapters either being devoted to, or including significant treatment of, the Cattell-Horn Gf-Gc and/or Carroll three- stratum theories in Flanagan, Genshaft and Harrison’s (1997) edited volume Contemporary intellectual assessment:  Theories, tests, and issues, a publication which, in turn, was also a major theory-to- practice bridging event (see section E3 in Table 1) for three reasons.
First, the CIA was the first book intended for university trainers and assessment practitioners that included chapters describing both the Cattell-Horn and Carroll models by the theorists themselves (Horn and Carroll).   For those unfamiliar with the Horn Gf-Gc theory chapter in the WJ-R technical manual (McGrew et al., 1991), the CIA book provided a long overdue introduction of the “state-of-the- art” of contemporary psychometric theories of intelligence to the professional keepers of the tools of the intelligence testing trade (e.g., school psychologists). 
Second, McGrew and Flanagan, while digesting the implication of the need for 3-S vision (as articulated by Carroll), and collaborating on a WJ-R/KAIT cross-battery confirmatory factor analysis study (see Flanagan & McGrew, 1998), realized that the prior Gf-Gc test classifications (Woodcock, 1990) described tests only at the broad or stratum II level, and they needed to  be “taken down to the next level”—to stratum I or the narrow ability level. In order to do so, a single taxonomy was needed.   Rather than picking Cattell-Horn or Carroll’s model over the other, a “Synthesized Carroll and Horn–Cattell Gf-Gc framework” (McGrew, 1997) was developed based on both Horn and Carroll’s writings and a review of a previously unpublished exploratory Schmid-Leiman factor analysis of the WJ-R completed by Carroll (see section F1 in Table 1).
Finally, included in the CIA was the first formal description of the assumptions, foundations, and operationalized set of principles for Gf-Gc cross-battery assessment (Flanagan & McGrew, 1997; see section F2 in Table 1).  The cross-battery seed planted by Woodcock (1990) had given birth.  The subsequent “spreading of the assessment gospel as per Gf-Gc cross-battery” (Flanagan & McGrew, 1997; McGrew & Flanagan, 1997; Flanagan et al., 2000; Flanagan & Ortiz, 2001; Flanagan, Ortiz, Alfonso & Mascolo, 2002; see section F4-F6 in Table 1) infused Gf- Gc theory into the minds of assessment practitioners and university training programs, regardless of their choice of favorite intelligence battery (e.g., CAS, DAS, K-ABC, SB4, WISC-III). The formalization of Gf-Gc cross- battery assessment, primarily as the result of the work of Flanagan, was another significant theory- to- practice bridging event.  Daniel (1997) described the cross- battery approach as “intriguing” and “creative work now being done to integrate and interpret all cognitive batteries within the framework of a single multifactor model” (p. 1043). 
Gf-Gc cross-battery assessment did not discriminate among test kits based on test name, heritage, publisher, type or color of carrying case, prominent authors (dead or alive), or presence or absence of manipulatives or a performance scale.  The cumulative impact of the introduction of Gf-Gc cross- battery assessment, following on the heels of the 1989 publication the Gf-Gc organized WJ-R and Carroll’s 1993 principia, established a Gf-Gc theory foothold in the field of applied intelligence testing.  The intelligence theory-to-practice gap had narrowed fast.  The CHC “tipping point” had been reached.  [Note.  The “tipping point” is the “moment of critical mass, the threshold, the boiling point” (Gladwell, 2000, p.12) where a movement, which has been building over time, generally in small groups and networks, begins to influence a much wider audience]
CHC: The rest of the story
The derivation of the name “Cattell-Horn-Carroll” (CHC) theory remains a mystery to many.  To the best of this author’s knowledge, the first formal published definition of CHC theory was presented in the WJ III technical manual (see McGrew & Woodcock, 2001; see section F5 in Table 1):
Cattell-Horn-Carroll theory of cognitive abilities.  An amalgamation of two similar theories about the content and structure of human cognitive abilities (J. B. Carroll & J. L. Horn, personal communication, July 1999).  The first of these two theories is Gf-Gc theory (Cattell, 1941; Horn, 1965) and the second is Carroll’s (1993) three-  stratum theory.  CHC taxonomy is the most comprehensive and empirically supported framework available for understanding the structure of human cognitive abilities (p. 9).
The first published record of the hyphenated linking of Cattell- Horn-Carroll is in Flanagan et al. (2000), were it was stated that “a first effort to create a single Gf-Gc taxonomy for use in the evaluation and interpretation of intelligence batteries was the integrated Cattell-Horn- Carroll model (McGrew, 1997)” (p. 28). Despite the foothold Gf-Gc theory had achieved in the field of applied intelligence testing prior to 1999, the term “Gf-Gc” was often meet with puzzled looks by recipients of psychological reports, sounded esoteric and non-meaningful, and continued to unintentionally convey the inaccurate belief that the theory was a two-factor model (Gf and Gc), despite the fact that it had evolved to an 8-9 broad ability model.  Having dealt with this communication problem since the publication of the WJ-R in 1989, Woodcock, together with the Stanford Binet Intelligence Scales—Fifth Edition (SB5; Roid, 2003) author, and staff from Riverside Publishing, meet with Horn and Carroll during a private meeting in Chapel Hill, NC, to seek a common, more meaningful, umbrella term that would recognize the strong structural similarities of their respective theoretical models, yet also recognize their differences.  Woodcock engaged Horn and Carroll in a sequence of conversations that resulted in a verbal agreement that the phrase “Cattell-Horn-Carrroll Theory of Cognitive Abilities” made significant practical sense, and, appropriately recognized the historical order of scholarly contribution of the three primary contributors (see section E4 in Table 1).  That was it.  “CHC” emerged from private personal communications in July, 1999, and seeped into subsequent publications. 
CHC theory represents both the Cattell-Horn and Carroll models, in their respective splendor.  Much like the phrase “information processing theories or models,” which provides an  overarching theoretical umbrella for a spectrum of very similar (yet different) theoretical model variations (Lohman, 2001), CHC theory serves the same function for the “variations on a Gf-Gc theme” by Cattell-Horn and Carroll, respectively.  Table 2 compares and contrasts the major similarities and differences between the Cattell- Horn Gf-Gc and Carroll three- stratum models.  As described above, the CHC model (Figure 1e) used extensively in applied psychometrics and intelligence testing during the past decade is a consensus model.  The specific organization and definition of broad and narrow CHC abilities is summarized in Table 3
In the next section, a review of the CHC-related structural factor analytic research published during the past decade is presented. The purpose of this review is to help the field iterate towards a more complete and better understanding of the structure of human cognitive abilities. 

[Note.  Carroll recognized the CHC umbrella terminology in his last publication (2003), although he also was a bit puzzled over the details of the origin of “so-called CHC (Catell-Horn-Carroll) theory of cognitive abilities” (p. 18). According to Carroll (2003), “even though I was to some extent involved in this change (as an occasional consultant to the authors and publisher), I am still not quite sure what caused or motivated it” (p. 18).  In a personal conversation with this author and Jack Carroll regarding this topic (at his daughters home in Fairbanks, Alaska on 5- 26-03), Carroll recognized the practical rational for the CHC umbrella term, but was planning to make it clear in the revision of his 1997 CIA chapter that although the CHC umbrella term may make practical sense, he felt strongly that human cognitive abilities consisted of at least three strata and that, in contrast to Horn’s position, that g exists.  He believed his last chapter publication (2003) provided convincing evidence for the existence of g.  Carroll wanted to make it clear that the overarching CHC umbrella did not reflect his agreement with Horn on all aspects of the structure of human cognitive abilities.]