Is a gin and tonic more like gin or tonic? A comparison of comorbid and non-comorbid anxiety disorder diagnostic pairs

• Investigated the degree to which pairs of clients who share the same set of diagnoses, but differ in terms of principal diagnosis showed similarities and differences from their non-comorbid, or “pure,” counterparts.
• 353 participants with diagnoses of either Panic Disorder only, Social Phobia only, Generalized Anxiety Disorder only, or some comorbid pair of the three were examined.
• Hierarchically opposing diagnostic pairs showed more overlap than differentiation with each other and with non-comorbid counterparts.
• Defining group comparisons by principal diagnoses may be invalid and misleading.

Despite findings indicating that anxiety disorders are more likely to co-occur with each other than occur in isolation, little research has explored precise areas of overlap and differentiation among comorbid pairs of anxiety disorders. Furthermore, many studies comparing phenomena across anxiety disorders define comparison groups based on principal diagnoses, with lesser regard for comorbid diagnoses, raising the question as to whether this is a valid approach to analyzing comparisons. To better understand the extent to which comparisons by principal diagnoses are valid, the current study investigated whether comorbid hierarchically opposing diagnostic pairs showed similarities and differences from their non-comorbid, or “pure”, counterparts on measures of clinician-rated functioning, specific symptoms, vulnerability factors, and demographic characteristics. The study included a total of 353 participants with diagnoses of either Panic Disorder (PD) only, Social Phobia (SP) only, Generalized Anxiety Disorder (GAD) only, or some comorbid pair of the three. Consistent with hypotheses, results demonstrated that hierarchically opposing diagnostic pairs showed more overlap than differentiation with each other and with non-comorbid counterparts on measures of a given specific non-comorbid diagnosis, indicating that defining comparisons by principal diagnoses may be invalid and misleading. The implications regarding the nosological structure of the DSM and research practice will be discussed.