Adil H. Haider

Erratum: Outcome of selective non-operative management of penetrating abdominal injuries from the North American National Trauma Database (British Journal of Surgery (2012) 99:1 (155-164)

Sir Ideally, a trial should have a single endpoint based on just one outcome measure. However, as the art of trial design has evolved, most large trials have a primary (composite) endpoint consisting of multiple outcome measures. In our trial both the prevalence of recurrent hyperthyroidism and changes in Graves’ ophthalmopathy were defined at the beginning of the trial as primary outcome measures because of their clinical importance in the field1. The sample size calculation was performed separately for each primary outcome measure as described in detail in the methods section. To detect an estimated absolute difference in recurrent hyperthyroidism rate of 5 per cent (a reduction from 5 per cent after bilateral subtotal thyroidectomy to 0 per cent after total thyroidectomy), 71 patients were required in each group to give the study a power of 80 per cent. On the other hand, to detect an estimated absolute difference in Graves’ ophthalmopathy progression rate of 8 per cent (a reduction from 16 per cent after bilateral subtotal thyroidectomy to 8 per cent after total thyroidectomy), 83 patients were required in each group to give the study a power of 80 per cent. Anticipating 15 per cent loss to follow-up, it was decided to include a total of 200 patients (100 in each group) in the trial. Thus, this study had a predefined power needed to detect an assumed difference in the primary outcome measures. M. Barczynski Third Department of General Surgery, Jagiellonian University Medical College, Krakow, Poland (e-mail: marbar@mp.pl) DOI: 10.1002/bjs.8829