Item response theory may account for unequal item weighting and individual-level measurement error in trials that use PROMs: a psychometric sensitivity analysis of the TOPKAT trial.

OBJECTIVES

To apply item response theory as a framework for studying measurement error in superiority trials which use patient-reported outcome measures (PROMs).

METHODS

We reanalyzed data from the The Total or Partial Knee Arthroplasty Trial, which compared the Oxford Knee Score (OKS) responses of patients undergoing partial or total knee replacement, using traditional sum-scoring, after accounting for OKS item characteristics with expected a posteriori (EAP) scoring, and after accounting for individual-level measurement error with plausible value imputation (PVI). We compared the marginalized mean scores of each group at baseline, 2 months, and yearly for 5 years. We used registry data to estimate the minimal important difference (MID) of OKS scores with sum-scoring and EAP scoring.

RESULTS

With sum-scoring, we found statistically significant differences in mean OKS score at 2 months (P = 0.030) and 1 year (P = 0.030). EAP scores produced slightly different results, with statistically significant differences at 1 year (P = 0.041) and 3 years (P = 0.043). With PVI, there were no statistically significant differences.

CONCLUSION

Psychometric sensitivity analyses can be readily performed for superiority trials using PROMs and may aid the interpretation of results.