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A
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Supported by at least two level I investigations
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B
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Supported by one level I investigation
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C
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Supported by level II investigations only
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|
D
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Supported by at least one level III investigation
|
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E
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Supported by level IV and V evidence
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Grading of evidence
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I
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Large randomized trials with clear-cut results; low risk of false-positive (alpha) error or false-negative (beta) error
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II
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Small randomized trials with uncertain results; moderate-to-high risk of false-positive (alpha) error and/or false-negative (beta) error
|
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III
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Nonrandomized, contemporaneous controls
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IV
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Nonrandomized, historical controls and expert opinion
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V
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Case series, uncontrolled studies, and expert opinion
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