Background. The literature documents that functional impairment is associated with affective disorders. Nevertheless, the choice among thorough, yet brief, well-validated assessments of functional impairment is limited. The objective of this study was to evaluate the psychometric properties of a brief scale of functional impairment, the Range of Impaired Functioning Tool (LIFE–RIFT).
Method. The study sample included subjects who presented with major depressive disorder at intake into the NIMH Collaborative Depression Study (CDS). The LIFE–RIFT is composed of items that are included in the Longitudinal Interval Follow-up Evaluation (LIFE). The reliability and validity were examined using data from LIFE–RIFT assessments conducted at four points in time: 6, 12, 18 and 24 months after intake into the CDS.
Results. Cross-sectional one factor models accounted for the covariance structure among the four scale items. A longitudinal factor model, with an invariant factor structure over time, also fitted the data well and indicated that the scale items are measures of one construct, namely functional impairment. The internal consistency reliability of the scale was supported with alpha coefficients ranging from 0·81 to 0·83. The inter-rater reliability intraclass correlation coefficient (ICC) was 0·94. Mixed-effect linear regression models showed that those in episode were significantly more impaired than those in recovery. Furthermore, in analyses of predictive validity, impairment was positively associated with subsequent recurrence and negatively associated with subsequent recovery.
Conclusions. This psychometric evaluation provides empirical support for the reliability and validity of the LIFE–RIFT, a brief measure of functional impairment.
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