Purpose: To determine the minimal clinically important difference (MCID) for the preference-based health-related quality of life instruments EQ-5D (U.S. population-based) and QWB in PTSD patients.
Methods: Two hundred patients aged 18 to 65 years with PTSD enrolled in a doubly randomized preference trial examining the treatment effect and treatment-preference effects between cognitive behavioral therapy and pharmacotherapy with sertraline and completed the EQ-5D and QWB at baseline and 10-week post-treatment. The anchor-based method utilized a Clinical Global Impression – Improvement (CGI-I), Clinical Global Impression – Severity, and PTSD Symptom Scale – Interview (PSS-I). We regressed the changes in EQ-5D and QWB scores on changes in the anchors using ordinary least squares regression. The slopes (beta coefficients) were the rates of change in the anchors as functions of change in EQ-5D and QWB, which represent our estimates of MCID. The distribution-based methods included: (1) 0.5 standard deviation (SD) of mean change in EQ-5D and QWB between baseline and post-treatment; and (2) 1 standard error of measurement (SEM) of EQ-5D and QWB.
Results: All three anchors (CGI-I, CGI-S, and PSS-I) correlated well with the EQ-5D and QWB (correlation coefficients ranged from 0.36 to 0.44). The anchor-based method estimated the MCID ranges of 0.05 to 0.08 for the EQ-5D and 0.03 to 0.05 for the QWB. The MCID ranges were higher with the distribution-based methods, ranging from 0.09 to 0.11 for the EQ-5D and 0.07 to 0.08 for the QWB.
Conclusions: The MCID ranges for the EQ-5D and QWB were determined in PTSD patients and consistent with previous studies in different disease states. The established MCID ranges of EQ-5D and QWB can be useful in selecting a preference-based health-related quality of life instruments for cost-effectiveness analysis.
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