Fluid intelligence shares closer to 60% of its variance with working memory capacity and is a better indicator of general intelligence

Article history: Received 30 May 2014 Received in revised form 18 August 2014 Accepted 15 September 2014 Available online 6 October 2014 A number of empirical studies have examined the association betweenworkingmemory capacity (WMC) and fluid intelligence (gf), with conclusions varying from constructs that are substantially distinct to constructs that are isomorphic. A review of the empirical literature suggests that these disparate conclusions are likely due to a number of factors, including the use of tests of varying quality, tests which share method variance, small sample sizes, and samples of varying representativeness of the population. Consequently, in this investigation, the association between WMC and gf was estimated based on well validated adult Wechsler scale subtests and a large, normative sample (N = 2200). Based on a correlated two-factor model, the correlation between WMC and gf was estimated at r = .77 (95% CI: .74/.80), suggesting a substantial level of shared variance, but a meaningful level of uniqueness, as well. Furthermore, based on a bifactor model and omega specific (ωs), bothWMC and gf were found to be associated with approximately equal standardized levels of unique common variance:WMCωs = .18 (95% CI: .12/.23) and gf ωs = .19 (95% CI: .13/.25). Finally, further evidence of divergent validity was obtained, as the gf subtests were observed to be more substantial indicators of general intelligence (g) than the WMC subtests. It is concluded that WMC and gf share approximately 60% of their true score variance, rather than the commonly cited 50%. Additionally, gf should be considered a better indicator of g than WMC on both empirical and theoretical grounds. © 2014 Elsevier Inc. All rights reserved.