Meta-analysis of the relationship between academic achievement and broad abilities of the Cattell-horn-Carroll theory

Interpretation of intelligence tests has changed over time, from a focus on the elevation of general ability in the early 1900s, to the shape and/or scatter of subtest and index scores in the mid-1900s to the early 2000s, and back to elevation today. The primary emphasis of interpretation now, however, is widely recommended to be on normative strengths and weaknesses of scores reflecting broad and narrow abilities in the Cattell-Horn-Carroll (CHC) theory (Schneider & McGrew, 2012). Decisions about which abilities are important to assess for the diagnosis of learning difficulties are based largely on literature reviews by Flanagan, Ortiz, Alfonso, and Mascolo (2006) and McGrew and Wendling (2010). These were narrative research syntheses, however, and did not attempt to estimate the magnitude of the relations between CHC abilities and academic achievement. The purpose of this study, therefore, was to conduct a meta-analysis to determine the effect size for these relations across age groups. Results of our analyses found that psychometric g and one or more broad cognitive abilities are substantially related to each area of academic achievement. Across all achievement domains and ages, g had by far the largest effect, with a mean effect size of r2 = 0.540. In fact, psychometric g explained more variance in academic outcomes than all broad abilities combined. Most broad abilities explained less than 10% of the variance in achievement and none explained more than 20%. Some age-related changes in cognitive ability-achievement relations were also observed. In sum, results of our meta-analysis support the interpretation of the overall score on intelligence tests as a measure of psychometric g for diagnosing difficulties in reading and mathematics, but only the interpretation of index scores measuring Comprehension-Knowledge (Gc) when diagnosing difficulties in reading. Implications of these results for research and practice are discussed.