Nested factors model of the WAIS-III subtests. The model depicts a “g” factor on which load all 11 subtests (names abbreviated), and 4 nested factors: Verbal Comprehension-(VC) specific, on which load vocabulary, similarities, information, and comprehension; Working Memory- (WM) specific, on which load arithmetic and digit span; Perceptual Organization- (PO) specific, on which load picture completion, block design, picture arrangement, and object assembly; and Perceptual Speed- (PS) specific, which has digit-symbol substitution as a single indicator. Because a two-indicator latent variable is not statistically identified when it does not correlate with any other variables in the model (Bollen, 1989), the loadings for the WM-specific variable were fixed at the values estimated in the full model that incorporated correlations with the executive function latent variables. Numbers above the ACEs for the latent variables are the percentages of those variables’ variances accounted for by genetic and environmental influences. The numbers occluding arrows are standardized factor loadings. Numbers under the lower ACEs are estimates for task-specific variances. Boldface type and solid lines indicate p < .05. Italic font indicates marginal significance for the .23 loading of the information subtest on the VC-specific variable (p = .066), the 18% specific C variance for the picture completion subtest (p = .055), and the 21% specific A variance for the picture arrangement subtest (p = .061).