First evidence on a general disease ("d") factor underlying psychopathology and physical illness in adolescents.

The coexistence of mental and physical health illnesses could be accounted for by an underlying general disease factor (termed d-factor), reflecting theoretical underpinnings based on possible genetic and pathophysiological overlapping mechanisms. This study evaluated whether the d-factor underlies mental and physical health illnesses in adolescents. A series of confirmatory factor analyses were conducted using data from 1120 adolescents. The proposed common underlying factor, we believe is the d-factor, was consistently present across different modeling approaches, including unidimensional, correlated-factor, and bifactor models. The best model fit was achieved with the bifactor model represented by mental, neurological, and psychical conditions tested. The first compelling evidence was provided supporting the existence of the transdiagnostic d-factor in youth, opening the door to innovative research of comorbid mental and physical health conditions.