The Internal State Scale: replication of its discriminating abilities in amultisite, public sector sample

Objective: The internal State Scale (ISS) is a self-report instrument that has been validated for discriminating mood states in patients with bipolar disorder. This study a) extends investigation to a multisite public sector sample and b) tests a revised scoring algorithm that formally identifies pa tients in mixed states. Methods: Eighty-Six patients with bipolar disorder from four Veterans Affai rs medical centers were assessed in a doss-sectional design. Physician-cond ucted semi-structured interviews used DSM-IV criteria to identify subjects as meeting criteria for euthymia, mania or hypomania, depression, or mixed state (mania or hypomania plus depression). A revised ISS scoring algorithm independently assigned mood state. Mean subscale scores were analyzed acro ss groups. Receiver-operating characteristic (ROC) curve analysis was condu cted to determine optimal algorithm structure. Results: Analysis of mean scores for the ISS subscales replicated original results for Activation. Well-Being, and Perceived Conflict. but indicated d ifferences from the original results for the Depression Index. The ROC curv e analysis identified optimal cut-off scores for the revised algorithm. The overall kappa score indicated moderate agreement between ISS and physician ratings of mood state, including mixed states. Limitations: The study used a sample consisting primarily of male veterans. Mood state was assigned by experts using expert clinician diagnosis. not s tructured interviews. Conclusion: The performance of the ISS in this multisite. public sector sam ple was similar to the performance in the initial research clinic sample. T his finding confirms the validity of the ISS as a discriminator of mood sta tes in bipolar disorder. The development of a revised scoring algorithm mak es feasible formal identification of mired episodes with the ISS.