Defining the minimal important change (MIC) and meaningful change value (MCV) for the Psoriatic Arthritis Disease Activity Score (PASDAS) in a routine practice cohort of patients with psoriatic arthritis.

The aim of the study was to determine the Minimal Important Change (MIC) values and Meaningful Change (MCV) values for the Psoriatic Arthritis Disease Activity Score (PASDAS) and the Standard Error of Measurement (s.e.m.) of the PASDAS. The routine practice data for 544 patients with PsA was available for analysis. An anchor-based method using linear regression analyses was used to determine the MICs and MCVs for the PASDAS. With this anchor-based method, we compared changes in the PASDAS score with an external reference (anchor). The anchor question inquired whether the patient's well-being had changed since their previous visit. It consisted of a 7-point Likert scale (range: very much improved to very much deteriorated). Interperiod correlation matrix analysis was performed to determine the s.e.m. The overall MIC and MCV for the PASDAS were 0.67 (95% CI: 0.55, 0.79) and 1.34 (95% CI: 1.21, 1.46), respectively. Results for improvement and deterioration were 0.65 (95% CI: 0.46, 0.83) and 0.71 (95% CI: 0.49, 0.93) for the MIC, respectively, and 1.29 (95% CI: 1.11, 1.48) and 1.42 (95% CI: 1.19, 1.64) for the MCV, respectively. The s.e.m. was determined at 0.81. The MIC for the PASDAS is a tool for physicians treating patients with PsA enabling them to give context to the patient's perspective of disease activity, while the MCV might aid the use of the PASDAS in PsA clinical trials.

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