. Author manuscript; available in PMC: 2019 Dec 5.

Published in final edited form as: Circulation. 2010 Jul 12;122(4):406–441. doi: 10.1161/CIR.0b013e3181e8edf1

Table 1.

Definition of Classes and Levels of Evidence Used in Dietary and Physical Activity Lifestyle Changes Recommendations²²⁶

Class I	Conditions for which there is evidence for and/or general agreement that the procedure or treatment is useful and effective.
Class II	Conditions for which there is conflicting evidence and/or divergence of opinion about the usefulness/efficacy of a procedure or treatment.
Class IIa	Weight of evidence or opinion is in favor of the procedure or treatment.
Class IIb	Usefulness/efficacy is less well established by evidence or opinion.
Class III	Conditions for which there is evidence and/or general agreement that the procedure or treatment is not useful/effective and in some cases may be harmful.
Level of Evidence A	Data derived from multiple randomized clinical trials.
Level of Evidence B	Data derived from a single randomized trial or nonrandomized studies.
Level of Evidence C	Expert opinion or case studies.