How to rate the level of evidence of research articles. From Oxford Centre for Evidence Based Medicine.

Evidence grading scale used by several family medicine and primary care journals. SORT addresses the quality, quantity, and consistency of evidence and allows authors to rate individual studies or bodies of evidence. Free online version - Am Fam Physician. 2004 Feb 1;69(3):548-556.

SORT Taxonomy Tables and strength-of-recommendation grades. Free PDF.

This article is the first of a series providing guidance for use of the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system of rating quality of evidence and grading strength of recommendations in systematic reviews, health technology assessments, and clinical practice guidelines addressing alternative management options. J Clin Epidemiol. 2011 Apr;64(4):383-94.

Revised in 2010, the CONSORT statement is a standard way for authors to prepare reports of trial findings, facilitating their complete and transparent reporting, and aiding their critical appraisal and interpretation. Includes a 25-item checklist and a flow diagram. The CONSORT Group is an international group of trialists, methodologists and medical journal editors.

STROBE stands for an international, collaborative initiative of epidemiologists, methodologists, statisticians, researchers and journal editors involved in the conduct and dissemination of observational studies, with the common aim of STrengthening the Reporting of OBservational studies in Epidemiology.

Full text online. Finkelstein A. Journal of Family Practice. 2005 Dec;54(12):1032.

The USPSTF assigns one of five letter grades (A, B, C, D, or I). The USPSTF changed its grade definitions based on a change in methods in May 2007 and again in July 2012, when it updated the definition of and suggestions for practice for the grade C recommendation.

Evidence ratings - for readers who want to learn more about EBM, and for authors preparing manuscripts for publication.