C Weak Recommendation There is at least moderate certainty based on evidence that there is a small net benefit. D Recommendation against There is at least moderate certainty based on evidence that it has no net benefit or that risks/harms outweigh benefits. E Expert Opinion ( There is insufficient evidence or evidence is unclear or conflicting, but this is what the committee recommends. )Net benefit is unclear. Balance of benefits and harms cannot be determined because of no evidence, insuffi- cient evidence, unclear evidence, or conflicting evidence, but the committee thought it was important to provide clinical guidance and make a recommendation. Further research is recommended in this area. N No Recommendation for or against ( There is insufficient evidence or evidence is unclear or conflicting. )Net benefit is unclear. Balance of benefits and harms cannot be determined because of no evidence, insuffi- cient evidence, unclear evidence, or conflicting evidence, and the committee thought no recommendation should be made. Further research is recommended in this area. The strength of recommendation grading system used in this guideline was developed by the National Heart, Lung, and Blood Institute s (NHLBI s) Evidence-Based Methodology Lead (with input from NHLBI staff, external methodology team, and guideline panels and work groups) for use by all the NHLBI CVD guideline panels and work groups during this project. Additional details regarding the strength of recommendation grading system are available in the online Supplement. a Net benefit is defined as benefits minus the risks/harms of the service/intervention. Table 2. 