Table 1.

Guidelines for Assigning the Level and Strength of Evidence and for Making Recommendations

Guideline	Definition
Levels of evidencea
Level I	Systematic reviews, meta-analyses, randomized controlled trials
Level II	Two groups, nonrandomized studies (e.g., cohort, case control)
Level III	One group, nonrandomized (e.g., before and after, pretest and posttest)
Level IV	Descriptive studies that include analysis of outcomes (e.g., single-subject design, case series)
Level V	Case reports and expert opinion that include narrative literature reviews and consensus statements
Strength of the evidence: Level of certaintyb
High	The available evidence usually includes consistent results from well-designed, well-conducted studies in representative primary care populations. These studies assess the effects of the preventive service on health outcomes. This conclusion is therefore unlikely to be strongly affected by the results of future studies.
Moderate	The available evidence is sufficient to determine the effects of the preventive service on health outcomes, but confidence in the estimate is constrained by such factors as the following: The number, size, or quality of individual studies Inconsistency of findings across individual studies Limited generalizability of findings to routine primary care practice Lack of coherence in the chain of evidence. As more information becomes available, the magnitude or direction of the observed effect could change, and this change may be large enough to alter the conclusion.
Low	The available evidence is insufficient to assess effects on health outcomes. Evidence is insufficient because of the following: The limited number or size of studies Important flaws in study design or methods Inconsistency of findings across individual studies Gaps in the chain of evidence Findings not generalizable to routine primary care practice Lack of information on important health outcomes. More information may allow estimation of effects on health outcomes.
Recommendationc
A	Strongly recommend that occupational therapy practitioners routinely provide the intervention to eligible clients. Good evidence was found that the intervention improves important outcomes and that benefits substantially outweigh harm.
B	Recommend that occupational therapy practitioners routinely provide the intervention to eligible clients. At least fair evidence was found that the intervention improves important outcomes and that benefits outweigh harm.
C	There is weak evidence that the intervention can improve outcomes, and the balance of the benefits and harms may result either in a recommendation that occupational therapy practitioners routinely provide the intervention to eligible clients or in no recommendation because the balance of the benefits and harm is too close to justify a general recommendation.
D	Recommend that occupational therapy practitioners do not provide the intervention to eligible clients. At least fair evidence was found that the intervention is ineffective or that harm outweighs benefits.
I	Insufficient evidence to recommend for or against routinely providing the intervention. Evidence that the intervention is effective is lacking, of poor quality, or conflicting, and the balance of benefits and harm cannot be determined.

^aSee Sackett, Rosenberg, Muir Gray, Haynes, & Richardson (1996). ^bThe U.S. Preventive Services Task Force (USPSTF; 1996) defines certainty as “likelihood that the USPSTF assessment of the net benefit of a preventive service is correct.” The net benefit is defined as benefit minus harm of the preventive service as implemented in a general, primary care population. The USPSTF assigns a certainty level based on the nature of the overall evidence available to assess the net benefit of a preventive service. ^cRecommendation criteria are based on the standard language of the Agency for Healthcare Research and Quality Series Commentary (Falck-Ytter, Schünemann, & Guyatt, 2010). Suggested recommendations are based on the available evidence and content experts’ opinions.