The Wechsler Preschool and Primary Scale of Intelligence--Fourth Edition (WPPSI-IV; Wechsler, 2012) represents a substantial departure from its predecessor, including omission of 4 subtests, addition of 5 new subtests, and modification of the contents of the 5 retained subtests. Wechsler (2012) explicitly assumed a higher-order structure with general intelligence (g) as the second-order factor that explained all the covariation of several first-order factors but failed to consider a bifactor model. The WPPSI-IV normative sample contains 1,700 children aged 2 years and 6 months through 7 years and 7 months, bifurcated into 2 age groups: 2:6-3:11 year olds (n = 600) and 4:0-7:7 year olds (n = 1,100). This study applied confirmatory factor analysis to the WPPSI-IV normative sample data to test the fit of a bifactor model and to determine the reliability of the resulting factors. The bifactor model fit the WPPSI-IV normative sample data as well as or better than the higher-order models favored by Wechsler (2012). In the bifactor model, the general factor accounted for more variance in every subtest than did its corresponding domain-specific factor and the general factor accounted for more total and common variance than all domain-specific factors combined. Further, the domain-specific factors exhibited poor reliability independent of g (i.e., ωh coefficients of .05 to .33). These results suggest that only the general intelligence dimension was sufficiently robust and precise for clinical use.

The development of factor models is inextricably tied to the history of intelligence research. One of the most commonly-cited scholars in the field is John Carroll, whose three-stratum theory of cognitive ability has been one of the most influential models of cognitive ability in the past 20 years. Nonetheless, there is disagreement about how Carroll conceptualized the factors in his model. Some argue that his model is best represented through a higher-order model, while others argue that a bi-factor model is a better representation. Carroll was explicit about what he perceived the best way to represent his model, but his writings are not always easy to understand. In this article, I clarify his position by first describing the details and implications of bi-factor and higher-order models then show that Carroll’s published views are better represented by a bi-factor model.

Chronic kidney disease (CKD) is characterized by a continuous reduction in kidney function, increased inflammation, and reduced antioxidant capacity. The objective of this study was to assess the effects of a herbal supplement on systemic inflammation and antioxidant status in non-dialysis CKD patients. Sixteen patients with CKD (56.0±16.0 yrs, 171.4±11.9 cm, 99.3±20.2 kg) were randomly chosen to receive a herbal supplement composed of Curcuma longa and Boswellia serrata , or placebo. Plasma levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), glutathione peroxidase (GPx), and serum C-reactive protein (CRP) were measured at baseline and 8 weeks. Baseline data demonstrated elevated inflammation and low antioxidant levels. A significant time effect (p=0.03) and time x compliance interaction effect (p=0.04) were observed for IL-6. No significant differences were observed for any other variables. This study demonstrates that mild and moderate CKD is associated with chronic inflammation and low antioxidant activity. Systemic inflammation and impaired antioxidant status may be greater in CKD populations with multiple comorbidities. Curcumin and Boswellia serrata are safe and tolerable and helped to improve the levels of an inflammatory cytokine.