The general factor of psychopathology: a comparison with the general factor of intelligence with respect to magnitude and predictive validity

In recent years, there has been a surge of interest in the general factor of psychopathology ("p"), which is intended to summarize broad psychiat-ric comorbidity into a single index. In this study, rather than attempting to validate this model using statistical techniques, we compared the magnitude (as indicated by the variance explained in the respective indicators) and the predictive validity of the "p" factor with those of the gen-eral factor of intelligence ("g"). To compare the magnitude, for "g", we analyzed fifteen Wechsler Adult Intelligence Scale subtests (N=1,200). For "p", we analyzed fourteen psychiatric diagnoses in Swedish adults (N=909,699), eight self- and parent-rated psychopathology scales in Swedish adolescents (N=2,069), and sixteen parent-rated psychopathology scales in Swedish children (N=14,589). To compare the predictive validity, we analyzed Swedish male military conscripts (N=414,595, mean age: 18.3 years) with measures on both "g" and "p" (derived from eight psychiatric diagnoses). We then examined their unique associations with three intelligence-related outcomes (annual income, highest education, and university entrance exam scores), and sixteen adverse outcomes (e.g., suicidal behavior, psychotropic medication prescription, and criminality) retrieved from registers (mean age at follow-up = 29.2 years). Results indicated that the magnitudes of "g" and "p" were very similar. Controlling for "p", "g" significantly predicted later education (standardized beta, β=0.38, SE=0.01) and university entrance exam scores (β=0.48, SE=0.01). Controlling for "g", "p" significantly predicted all adverse outcomes (mean β=0.32; range: 0.15 to 0.47). These findings support the notion that psychopathology indicators can be combined into a single score, similar to how intelligence subtests are combined into a general intelligence score. This "p" score might supplement specific diagnoses when formulating a management plan and predicting prognosis.

Is there a genetic correlation between general factors of intelligence and personality?

We tested a hypothesis that there is no genetic correlation between general factors of intelligence and personality, despite both having been selected for in human evolution. This was done using twin samples from Australia, the United States, the Netherlands, Great Britain, and Croatia, comprising altogether 1,748 monozygotic and 1,329 same-sex dizygotic twin pairs. Although parameters in the model-fitting differed among the twin samples, the genetic correlation between the two general factors could be set to zero, with a better fit if the U.S. sample was excepted.