Randomized clinical trial of bilateral subtotal thyroidectomy versus total thyroidectomy for Graves' disease with a 5-year follow-up (Br J Surg 2012; 99: 515–522)

Sir I read this original article with great interest. The authors have used two primary outcomes in the trial, the prevalence of recurrent hyperthyroidism and changes in Graves' ophthalmopathy. They concluded that total thyroidectomy prevented recurrent hyperthyroidism (P = 0·002), but did not prevent progression of the Graves' ophthalmopathy (P = 0.586). Randomized controlled trials (RCTs) assess outcomes for which the interventions are being compared. There can be several outcomes in an RCT and these are divided into two types: primary and secondary. A primary outcome is the most important prespecified endpoint used to reach a decision regarding the overall result of the trial. It also serves as the basis for calculation of the sample size for a particular RCT. All other outcomes are considered secondary. So, a RCT must have only one primary outcome, which should be disclosed explicitly at the beginning of the trial1.