Minimal clinically important differences in SF-36 global score: Current value in orthopedic oncology

Abstract

The SF-36 is widely used to evaluate the health-related quality of life (HRQoL) of patients with musculoskeletal tumors. Instead of typical methods, calculating the SF-36 Global Score has recently become an increasingly common reporting approach. However, numerical changes lack clear clinical relevance. The minimal clinically important difference (MCID) is useful for interpreting changes in functional scores by defining the smallest change patients may perceive as clinically meaningful. The aim of this study is to determine the MCID of the SF-36 Global Score in orthopedic oncology patients, which has not been reported to date. Three-hundred ten patients who underwent surgery and completed two surveys during postoperative follow-up were reviewed. The two most common methods for calculating the SF-36 Global Score were used: (1) anchor-based methods and receiver operating characteristic analysis based on one-half of the SD of change score and standard error of measurement at baseline and; (2) distribution-based methods. Using anchor-based methods, the MCIDs of SF-36 Global Scores #1 and #2 were 2.7 (area under the curve [AUC] = 0.85) and 2.5 (AUC = 0.79) for improvement, and -1.5 (AUC = 0.81) and -0.6 (AUC = 0.83) for deterioration, respectively. Using distribution-based methods, the MCIDs of SF-36 Global Scores #1 and #2 were 4.1 and 4.4 by half SD, and 4.1 and 4.5 by standard error of measurement, respectively. Our findings provide benchmark values, which can serve as a reference for future studies in musculoskeletal tumor patients using the SF-36 Global Score as a single measure for HRQoL.

Keywords: SF-36 Global Score; anchor-based method; distribution-based method; health-related quality of life (HRQoL); minimal clinically important difference (MCID); sarcoma.

Conflict of interest statement

Competing interests

The authors declare that they have no competing interests.

© 2020 Orthopaedic Research Society. Published by Wiley Periodicals LLC.

Figures

Figure 1.

Flow diagram showing patient eligibility criteria for analysis.

Figure 2.

Box-and-whiskers plots demonstrate the relationship between change of SF-36 Global Scores #1 (A) and #2 (B) and also displays answers to each anchor question.

Figure 2.

Box-and-whiskers plots demonstrate the relationship between change of SF-36 Global Scores #1 (A) and #2 (B) and also displays answers to each anchor question.

Figure 3.

The ROC curves for improvement (A) and deterioration (B) plots the true positive rate (sensitivity) against the false-positive rate (1 - specificity) for SF-36 Global Scores #1 (green line), and #2 (blue line).

Figure 3.

The ROC curves for improvement (A) and deterioration (B) plots the true positive rate (sensitivity) against the false-positive rate (1 - specificity) for SF-36 Global Scores #1 (green line), and #2 (blue line).