Anchor questions to improve patient-reported outcome measure interpretability in patients undergoing knee or hip arthroplasty - a mixed-methods content validity, construct validity, and reliability study

PURPOSE: To explore content validity, construct validity, and reliability of anchor questions used to determine minimal important change (MIC), patient acceptable symptom state (PASS) and treatment failure (TF) in patients undergoing knee or hip arthroplasty.

METHODS: A mixed-methods study from one public hospital. Evaluation of content validity involved applying thematic analysis to data from think-aloud interviews. To ascertain construct validity and reliability, we focused on patients who underwent surgery between 2016 and 2022 and had responded to preoperative and either 3-, 12- or 24-month postoperative questionnaires. Confirmatory factor analysis (CFA) was employed to assess present state bias (PSB), model fit, and reliability of the anchor questions.

RESULTS: We conducted 18 interviews with patients aged 52 to 84 (10 female). Based on seven emerging themes from the content validity analysis, MIC and PASS anchor questions were considered relevant and comprehensible, while the TF anchor question had several problems. Data from 1197 to 2207 patients, with 3-, 12-, or 24-month postoperative responses, were used to evaluate construct validity. The median age was 69-70 years (56-59% female). PSB for MIC was between 54 and 73%, and reliability for the anchor questions was between 0.52 and 0.80 for all time points. The CFA models varied between good and poor fit.

CONCLUSION: The MIC and PASS anchor questions demonstrated a high degree of content validity, while it was questionable for TF. Construct validity was considered good to poor for PASS, but patients may consider their present state more than their preoperative state when responding to the MIC. Reliability was considered acceptable in both MIC and PASS.