Equipercentile equating of scores from common patient-reported outcome measures of physical function in patients with cancer

OBJECTIVE: To provide equipercentile equating of physical function (PF) scores from frequently used patient-reported outcome measures (PROMs) in cancer patients to facilitate data pooling and comparisons.

STUDY DESIGN AND SETTING: Adult cancer patients from five European countries completed the European Organization for Research and Treatment of Cancer (EORTC) computer adaptive test (CAT) Core, EORTC Quality of Life Questionnaire Version 3.0 (QLQ-C30), Functional Assessment of Cancer Therapy - General (FACT-G), 36-item Short Form Health Survey (SF-36), and the Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function 20a short form. The R package "equate" was used to establish conversion tables of PF scores on those measures with a bivariate rank correlation of at least 0.75.

RESULTS: In total, 953 patients with cancer (mean age 58.9 years, 54.7% men) participated. Bivariate rank correlations between PF scores from the EORTC CAT Core, EORTC QLQ-C30, SF-36, and PROMIS were all above 0.85, but below 0.69 for the FACT-G. Conversion tables were established for all measures but the FACT-G. These tables indicate which score from one PROM best matches the score from another PROM and provide standard errors of converted scores.

CONCLUSION: Our analysis indicates that linking of PF scores from both EORTC measures (CAT and QLQ-C30) with PROMIS and SF-36 is possible, whereas the physical domain of the FACT-G seems to be different. The established conversion tables may be used for comparing results or pooling data from clinical studies using different PROMs.