Figure 1.

Parameters F1–F3 and parameters E1–E3 are estimates from Cholesky models estimating the familial and child-specific environmental factors across IQ, ADHD and Reading Difficulties Questionnaire (RDQ), respectively. Significant paths (p<0.05) are indicated as solid lines and non-significant paths (p≥0.05) are indicated as dotted lines.

Note: Parameters F1–F3 represent familial influences on and between the traits. f_1,1 represents the sum of the familial influences underlying IQ. f_2,1 represents the familial influences from IQ that are also shared with ADHD, while parameter f_2,2 represents those familial influences that underlie ADHD, and are not shared with IQ. The sum of familial influences underlying ADHD is therefore the sum of f_1,1 (those shared with IQ) and f_2,2 (those not shared with IQ). The same inferences apply to RDQ, such that f_3,1 represents familial influences underlying RDQ that are shared with ADHD (and to some extent ADHD), f_3,2 represents familial influences shared between ADHD and RDQ only, and f_3,3 represents familial influences specific to RDQ only. The sum of these three paths represents the sum of all familial influences underlying RDQ. The same inferences can be made for the E parameters, which represent child-specific environmental influences (and subsume any measurement error).