Journal Article

Item response theory validation of the Oxford knee score and Activity and Participation Questionnaire: a step toward a common metric

Scott, Chloe E.H., MacDonald, Deborah, Khatri, Chetan, Metcalfe, Andrew J., Rodrigues, Jeremy N., Clement, Nick, Harrison, Conrad J.

2024

Overview

The Oxford knee score (OKS) and OKS Activity and Participation Questionnaire (OKS-APQ) are patient-reported outcome measures used to assess people undergoing knee replacement surgery. They have not explicitly been tested for unidimensionality (whether they measure one underlying trait such as ‘knee health’). This study applied item response theory (IRT) to improve the validity of the instruments to optimize for ongoing use. Participants undergoing primary total knee replacement (TKR) provided preoperative and postoperative responses for OKS and OKS-APQ. Confirmatory factor analysis (CFA) were performed on the OKS and OKS-APQ separately and then on both when pooled into one. An IRT model was fitted to the data. 2972 individual response patterns were analyzed. CFA demonstrated that when combining OKS and OKS-APQ as one instrument, they measure one latent health trait. A user-friendly, free-to-use, web app has been developed to allow clinicians to upload raw data and instantly receive IRT scores. The OKS and OKS-APQ can be combined to use effectively as a single instrument (producing a single score). For the separate OKS and OKS-APQ the original items and response options can continue to be posed to patients, and this study has confirmed the suitability of IRT-weighted scoring. Applying IRT to existing responses converts traditional sum scores into continuous measurements with greater granularity, including individual measurement error. •The Oxford knee score and Oxford knee score-Activity and Participation Questionnaire measure one latent trait, coined as ‘knee health’.•Combining scores can potentially overcome floor and ceiling effects.•The presented web app can convert scores from tradition sumscore to item response theory scores.•Item response theory accounts for missing data, existing datasets can retain value.

• Publisher: Elsevier Inc,Elsevier Limited
• Subject: Aged / Applications programs / APQ / Arthroplasty, Replacement, Knee / Clinical outcomes / Design optimization / Discriminant analysis / Factor analysis / Factor Analysis, Statistical / Female / Graded response model / Humans / Internal Medicine / Item response theory / Joint replacement surgery / Knee / Likert scale / Male / Middle Aged / Missing data / OKS / Orthopaedic implants / Osteoarthritis, Knee - surgery / Oxford activity and participation questionnaire / Oxford knee score / Patient Reported Outcome Measures / Psychometrics / Quantitative psychology / Questionnaires / Reproducibility of Results / Surveys and Questionnaires - standards