Nonresponder bias in hand surgery: analysis of 1945 cases lost to follow-up over a 6-year period.

The primary aim of this study was to identify factors associated with nonresponse to routinely collected patient-reported outcome measures (PROMs) after hand surgery. The secondary aim was to investigate the impact of nonresponder bias on postoperative PROMs. We identified 4357 patient episodes for which the patients received pre- and 1-year postoperative questionnaires. The response rate was 55%. Univariate and regression analyses were undertaken to determine factors predicting nonresponse. We developed a predictive model for the postoperative Quick version of the Disabilities of the Arm, Shoulder, and Hand (QuickDASH) scores for nonresponders using imputation. Younger age, increasing deprivation, higher comorbidity, worse preoperative QuickDASH scores and unemployment predicted nonresponse. No significant difference in mean postoperative QuickDASH score was observed between the responders, and the scores for the responders combined with the predicted scores for the nonresponders. Preoperative function was the primary predictor of postoperative outcome. These results challenge the dogma that 'loss to follow-up' automatically invalidates the results of a study.Level of evidence: III.