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The Patient Global Impression of Change (PGIC) measure has frequently been used as an indicator of meaningful change in treatments for chronic pain. However, limited research has examined the validity of PGIC items despite their wide adoption in clinical trials for pain. Additionally, research has not yet examined predictors of PGIC ratings following psychologically based treatment for pain. The purpose of the present study was to examine the validity, factor structure, and predictors of PGIC ratings following an interdisciplinary psychologically based treatment for chronic pain. Patients with chronic pain (N = 476) completed standard assessments of pain, daily functioning, and depression before and after a 4-week treatment program based on the principles of acceptance and commitment therapy. Following the program, patients rated 1 item assessing their impression of change overall and several items assessing their impression of more specific changes: physical and social functioning, work-related activities, mood, and pain. Results indicated that the global and specific impression of change items represent a single component. In the context of the acceptance and commitment therapy–based treatment studied here, overall PGIC ratings appeared to be influenced to a greater degree by patients' experienced improvements in physical activities and mood than by improvements in pain. The findings suggest that in addition to a single overall PGIC rating, domain-specific items may be relevant for some treatment trials. Perspective This article reports on the validity and predictors of patients' impression of change ratings following interdisciplinary psychologically based treatment for pain. In addition to a single overall PGIC rating, domain-specific items may be important for clinicians and researchers to consider depending on the focus of treatment. [ABSTRACT FROM AUTHOR]