Development and validation of 21-item outcome inventory (OI-21)

BACKGROUND: Outcome measurement is important for monitoring patients’ progress. The study aimed to develop an outcome inventory (OI) for clinical use in routine practice in psychiatric services and to examine the psychometric properties of the newly developed OI. METHODS: 48 items measuring anxiety, depression, interpersonal difficulties, and somatization were collected. Factor analysis was used to reduce the number of items. The final OI consisting of 21 items was then examined for psychometric properties among 1302 participants, 880 were nonclinical and 422 clinical patients. Tests included confirmatory factor analysis, internal consistency, test-retest reliability, convergent and discriminant validity, and diagnostic ability for major depression. Responsiveness was compared between baseline and 3-month follow-up. RESULTS: Confirmatory factor analysis revealed the OI-21 demonstrated the designated four components. Cronbach's alpha was good to excellent for all subjects with good test-retest reliability, concurrent validity, convergent and discriminant validity. It demonstrated area under the ROC curve of 0.89 indicating good diagnostic performance. Sensitivity to change after 3 months was observed in both types of treatment. However, interpersonal difficulties were sensitive to change in those receiving additional psychotherapy. CONCLUSION: OI-21 demonstrated its validity, reliability, and sensitivity to change. It constitutes a promising tool for outcome assessment in nonclinical populations and among psychiatric patients.