Construct Validity and Reliability of a Bipolar Disorder Symptoms Inventory (BDSI)

Background: In order to assess the symptoms of bipolar disorder and to construct an inventory, this study was performed on 108 people from two sample groups (53 non-clinical participants) (55 participants with bipolar disorder) who were selected by a purposive sampling method. Methods: In order to evaluate the reliability of this 74-item of the inventory, the method of internal consistency and temporal stability was used. Factor analysis and content, structure and convergent validity of the bipolar disorder symptom inventory were also examined. Results: Cronbach’s alpha coefficient was 0.91 (N = 55, in the bipolar sample) and 0.83 (N = 53, in the non-clinical sample), respectively, and P<0.05, which indicated the appropriate internal consistency of this instrument. Also, to evaluate the temporal stability of the inventory, 35 participants (a combination of both non-clinical groups and participants with bipolar disorder) were randomly selected from 108 participants and the inventory for the second time and seven weeks after the first time was filled. The correlation coefficient of the total scores of the inventory between the first and second time was r = 0.91, P <0.01, which indicates a very good stability of this inventory. The convergent validity of this inventory was assessed with the Career Problems Inventory–Bipolar Disorder form (CPI-BD) and the correlation of the total score of the career problems inventory–bipolar disorder form with the total score of the Bipolar Disorder Symptoms Inventory (BDSI) in non-clinical sample and bipolar sample, respectively was (r = 66), P <0.0001, N = 53 and (r = 66, P <0.0001, N = 53). In factor analysis of the inventory using varimex rotation, eight subscales were extracted, which include: communication problems, neuroticism, change seeking, instability, restlessness, euphoria, dysfunctional problem perception and depressive thoughts. Conclusion: The bipolar disorder symptom inventory is a valid and reliable tool to assess and diagnose bipolar disorder symptoms.