Elements

Strong

Moderate

Limited

Expert Opinion Only

Grade Not Assignable

Quality

· Scientific rigor and validity

· Study design and execution

Studies of strong design

Free from design flaws, bias, and execution problems

Studies of strong design with minor methodological concerns

OR only studies of weaker study design for question

Studies of weak design for answering the question OR inconclusive findings due to design flaws, bias, or execution problems

No studies available

Conclusion based on usual practice, expert consensus, clinical experience, opinion, or extrapolation from basic research

No evidence that pertains to question being addressed

Consistency

· Consistency of findings across studies

Findings generally consistent in direction and size of effect or degree of association, and statistical significance with minor very exceptions

Inconsistency among results of studies with strong design,

OR consistency with minor exceptions across studies of weaker design

Unexplained inconsistency among results from different studies,

OR single study unconfirmed by other studies

Conclusion supported solely by statements of informed nutrition or medical commentators

NA

Quantity

· Number of studies

· Number of study participants

One large study with a diverse population or several good quality studies

Large number of subjects studied

Studies with negative results have sufficiently large sample size for adequate statistical power

Several studies by independent investigators

Doubts about adequacy of sample size to avoid Type I and Type II error

Limited number of studies

Low number of subjects studied and/or inadequate sample size within studies

Unsubstantiated by published research studies

Relevant studies have not been done

Impact

· Importance of studied outcomes

· Magnitude of effect

Studied outcome relates directly to the question

Size of effect is clinically meaningful

Significant (statistical) difference is large

Some doubt about the statistical or clinical significance of the effect

Studied outcome is an intermediate outcome or surrogate for the true outcome of interest

OR size of effect is small or lacks statistical and/or clinical significance

Objective data unavailable

Indicates area for future research

Generalizability

· Generalizability to population of interest

Studied population, intervention and outcomes are free from serious doubts about generalizability

Minor doubts about generalizability

Serious doubts about generalizability due to

narrow or different study population, intervention or outcomes studied

Generalizability limited to scope of experience

NA