Table 2.

Possible Explanations for the Co-occurrence of Two or more Comorbid Psychiatric Disorders

Both Disorders are Reflection of the Same Phenomenon

1. Both conditions are reflections of the same phenomenon.

2. One of the two conditions is a mere reflection of the other.

3. One of the two induces changes that lead to the other.

Common Factor for Both Disorders

1. Vulnerability hypothesis.

Artefact of Diagnostic Criteria

1. Comorbidity due to overlapping criteria.

2. Comorbidity due to one disorder encompassing the other.

The Comorbid Disorders are Two Separate Entities

1. They can be either one or the other.

2. They may appear together (comorbidity viewpoint).

3. Each can appear at threshold or subthreshold level. Any combination is possible (mixture subsyndromal viewpoint).

4. Comorbidity is a common final pathway of two distinct conditions.

Adapted from Klein and Riso (22).