| Level I |
Provides strong evidence in support of the statement. The design of the study allowed the issue to be
addressed, and the study was performed in the population of interest, executed in such a manner as to produce accurate
and reliable data, and analyzed using appropriate statistical methods. The study produced either statistically
significant results or showed no difference in results despite a design specified to have high statistical power and/or
narrow confidence limits on the parameters of interest.
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| Level II |
Provides substantial evidence in support of the statement. Although the study has many of the
attributes of one that provides Level I support, it lacks one or more of the components of Level I.
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| Level III |
Provides a consensus of expert opinion in the absence of evidence that meets Levels I and II.
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Level I, defined as most important
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Level II, defined as moderately important
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Level III, defined as relevant but not critical
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