Background: Anxiety is one of the most prevalent mental disorders and accounts for substantial disability as well as increased health care costs. This study examines the minimally important difference (MID) and responsiveness of 6 commonly used anxiety scales.
Methods: The sample comprised 294 patients from 6 primary care clinics in a single VA medical center who were enrolled in a telecare trial for treatment of chronic musculoskeletal pain and comorbid depression and/or anxiety. The measures assessed were the Patient Reported Outcomes Measurement Information System (PROMIS) 4-item, 6-item, and 8-item anxiety scales; the Generalized Anxiety Disorder 7-item scale (GAD-7); the Symptom Checklist anxiety subscale (SCL); the Posttraumatic Stress Disorder Checklist (PCL); the Short Form (SF)-36 Mental Health subscale; and the SF-12 Mental Component Summary (MCS). Validity was assessed with correlations of these measures with one another and with measures of quality of life and disability. MID was estimated by triangulating several methods. Responsiveness was evaluated by comparing: (a) the standardized response means for patients who reported their mood as being better, the same, or worse at 3 months; (b) the area under the curve for patients who had improved (better) versus those who had not (same/worse).
Results: Convergent and construct validity was supported by strong correlations of the anxiety measures with one another and moderate correlations with quality of life and disability measures, respectively. All measures differentiated patients who reported global improvement at 3 months from those who were unchanged, but were less able to distinguish worsening from no change. The area under the curves showed comparable responsiveness of the scales. The estimated MID was 4 for the PROMIS scales; 3 for the GAD-7; 6 for the PCL; 9 for the SF-36 mental health subscale; 5 for the MCS score, and 0.3 for the SCL anxiety scale.
Conclusions: Six commonly used anxiety scales demonstrate similar responsiveness, and estimated MIDs can be used to gauge anxiety change in clinical research and practice.