Development and psychometric evaluation of the Bipolar Functional Status Questionnaire (BFSQ)

Abstract

Persistently impaired psychosocial functioning has been recognized in many individuals with bipolar disorder. However, existing measures of functional disability have been adapted for use in bipolar disorder based mainly on those developed for use in other conditions. The present study involved the development and validation of a new patient self-report measure specific to bipolar disorder, the Bipolar Functional Status Questionnaire (BFSQ). Relevant constructs were identified, evaluated, and refined through an expert advisory panel in conjunction with patient interviews. Questionnaire items were vetted through iterative patient interviews. Psychometric properties were determined based on patient responses from implementation of the proposed 33-item questionnaire in an 11-site study of 596 patients with bipolar disorder across varied phases of illness. Eight constructs were identified as fundamental to functional status in bipolar disorder: cognitive function, sleep, role functioning, emotional functioning, energy/vitality, social functioning, personal management, and sexual functioning. Psychometric validation supported item reduction to a 24-item unidimensional scale, with high internal consistency (coefficient alpha's = 0.93-0.95), high test-retest reliability (intraclass correlation coefficient = 0.86, 95% confidence interval = 0.82-0.89), strong convergent validity with other functional disability measures (r's > 0.70), and highly significant discriminant validity across illness phases, with large effect sizes (Cohen's d > 0.70). The BFSQ is a psychometrically sound self-report measure that can be used to effectively quantify functional status across different clinical states in patients with bipolar disorder.