Context: Grading scientific evidence is a critical step in developing practice guidelines and quality performance measures.
General question: What is the most useful way to grade evidence?
Specific question: How should we grade the recommended clinical practices for patients with diabetes?
Standard approach: Hierarchical grading systems (e.g., grades I, II, and III), such as that used by the U.S. Preventive Services Task Force, have traditionally been used to rank the research designs of studies that support a particular clinical practice.
Potential difficulties: Many studies that support the clinical practices of diabetes care do not clearly conform to the categories traditionally used in hierarchical grading systems. As a result, there is a tendency to inaccurately characterize the level of evidence, leading to the phenomenon of evidence inflation or evidence deflation. To avoid exaggerating the evidence, important sources of information may be excluded, resulting in an understatement of the available supporting evidence.
Alternate approach: This paper offers a more descriptive typologic system that uses the study design and an explanatory modifier to grade the evidence supporting the clinical practices of diabetes care. The study grades are randomized, controlled trial (RCT); RCT-embedded component; RCT-treatment only; RCT-different population; observational study-risk factor; and expert opinion. Using this grading system, the authors were able to more accurately describe the best available evidence supporting the clinical practices of diabetes care.