Data Errors in Table: In the Original Contribution entitled “Scientific Evidence Underlying the ACC/AHA Clinical Practice Guidelines,” published in the February 25, 2009, issue (2009;301[8]:831-841), Table 1 contains data errors. For “Unstable angina” the row for 2007 should report the following data: Class I, 187/298; Class II, 82/298; and Class III, 29/298. The percentages shown in this row are correct. In the row “Change in No. of recommendations” for disease guidelines, correct numbers are +109 (Class I), +137 (Class II), and +25 (Class III). Near the bottom of Table 1, under “Summary of all guidelines,” the row “Change in No. of recommendations” should report +315 (Class I), +248 (Class II), and +80 (Class III). Also in Table 1, under “Interventional guidelines” the row 2004 for CABG should report the denominator as 84 (not 56). The percentages shown are correct. As a consequence, on page 833 in the first column, the sentence should read, “The raw increase in number of recommendations was higher for disease-based guidelines (271 additional recommendations) and diagnostic procedure–based guidelines (242 additional recommendations) than for interventional procedure–based guidelines (130 additional recommendations).”