Background: Although the diagnostic reliability of major depression and mania has been well established, that of hypomania and bipolar II (BPII) disorder has not. This remains an important issue for clinicians, especially for those undertaking genetic studies of BP disorder since bipolar I (BPI) and BPII disorders often cluster in the same families. We have assessed our diagnostic reliability of BP disorders, recurrent unipolar disorder, and their constituent episodes (major depression, mania, and hypomania) using interview and best-estimate diagnostic procedures used in a genetic study of families with BPI disorder.
Methods: Reliability was assessed for (1) co-rated Schedule for Affective Disorders and Schizophrenia-Lifetime version interviews of 37 subjects including 15 with BP disorders; (2) test-retest Schedule for Affective Disorders and Schizophrenia-Lifetime version interviews of 26 subjects including 13 with BP disorders; and (3) best-estimate diagnoses made by 2 noninterviewing psychiatrists on 524 subjects in a genetic linkage study of BPI disorder. Diagnoses were based on Research Diagnostic Criteria for a Selected Group of Functional Disorders, except that recurrent major depression as well as hypomania was required for a diagnosis of BPII disorder.
Results: On co-rated interviews, we observed complete agreement between interviewers for diagnosing major depressive, manic, and hypomanic episodes. For test-retest interviews, the Cohen kappa coefficients were 0.83 for manic, 0.72 for hypomanic, and 1.0 for major depressive episodes. At the best-estimate level, the Cohen kappa coefficients were 0.99 for BPI, 0.99 for BPII, and 0.98 for recurrent unipolar disorder.
Conclusion: Good interrater reliability for BPII can be achieved when the interviews and best-estimate diagnoses are done by experienced psychiatrists.