Fig. 2.

How comorbidity can arise according to the network approach. Disorder X consists of the eight symptoms X1–X5 and B1–B3, and disorder Y consists of the eight symptoms Y1–Y5 and B1–B3. B1–B3 are bridge symptoms that feature in both diagnoses. In this case, a person first develops X3 in response to an environmental stressor E, then symptoms of disorder X, then bridge symptoms B, and finally symptoms of disorder Y