Applying Classification of Recommendations and
Level of Evidence
Estimate of Certainty (Precision) of Treatment Effect
Size of Treatment Effect
CLASS I
Benefit >>> Risk
Procedure/Treatment
SHOULD be
performed/
administered
CLASS IIa
Benefit >> Risk
Additional studies with
focused objectives needed
IT IS REASONABLE
to perform procedure/
administer treatment
LEVEL A
Multiple populations
evaluateda
▪Recommendation that ▪Recommendation in favor
procedure or treatment of treatment or procedure
is useful/effective
being useful/effective
Data derived from
multiple randomized
clinical trials or metaanalyses
LEVEL B
Limited populations
evaluateda
▪Sufficient evidence
from multiple
randomized trials or
meta-analyses
▪Recommendation that
procedure or treatment
is useful/effective
Data derived from a
single randomized trial
or nonrandomized
studies
LEVEL C
Very limited populations
evaluateda
Only consensus opinion
of experts, case studies,
or standards of care
▪Evidence from single ▪Some conflicting evidence
randomized trial or
from single randomized trial
nonrandomized studies or nonrandomized studies
▪Some conflicting evidence
from multiple randomized
trials or meta-analyses
▪Recommendation in favor
of treatment or procedure
being useful/effective
▪Recommendation that ▪Recommendation in favor
procedure or treatment of treatment or procedure
is useful/effective
being useful/effective
▪Only expert opinion,
case studies, or
standard of care
Suggested phrases
should
for writing
is recommended
recommendations:
is indicated
is useful/effective/
beneficial
Comparative effectiveness treatment/strategy
phrasesb:
A is recommended/
indicated in preference
to treatment B
treatment A should be
chosen over treatment B
▪Only diverging expert
opinion, case studies, or
standard of care
is reasonable
can be useful/effective/
beneficial
is probably recommended or
indicated
treatment/strategy A is
probably recommended/
indicated in preference to
treatment B
it is reasonable to choose
treatment A over treatment B
A recommendation with Level of Evidence B or C does not imply that the recommendation is
weak. Many important clinical questions addressed in the guidelines do not lend themselves to
clinical trials. Although randomized trials are unavailable, there may be a very clear clinical
consensus that a particular test or therapy is useful or effective.
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