A reference is omitted from the seventh sentence of the first paragraph under the subheading “Outcome measures and follow-up” in the Methods.The sentence should read: An adjudication committee whose members were unaware of the patients’ treatment assignments confirmed that all relapses met the study definition of relapse (Aaron et al., 2003).The reference is: Aaron SD, Vandemheen KL, Hebert P, Dales R, Stiell IG, Ahuja J, et al. Outpatient Oral Prednisone after Emergency Treatment of Chronic Obstructive Pulmonary Disease. N Engl J Med 2003; 348:2618–25.