In the “AFP Journal Club,” titled “Usefulness of Procalcitonin Measurement in Reducing Antibiotic Use and Identifying Serious Bacterial Illness,” (July 15, 2011, page 177), the terms “sensitivity and specificity” were used instead of “positive predictive value” in the last sentence of the second paragraph of the left-hand column on page 178. This sentence should have read: “To state this succinctly, the positive predictive value of a test changes depending on the prevalence of disease in the population in which it is used.” The article has been corrected online.