Estimate of Certainty (precision) 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
evaluated*
▪Recommendation that ▪Recommendation in favor of
procedure or treatment treatment or procedure being
is useful/effective
useful/effective
Data derived from
multiple randomized
clinical trials or metaanalyses
LEVEL B
Limited populations
evaluated*
▪Sufficient evidence
from multiple
randomized trials or
meta-analyses
▪Recommendation that
procedure or treatment
is useful/effective
▪Some conflicting evidence
from multiple randomized
trials or meta-analyses
Data derived from a
single randomized trial or
nonrandomized studies
LEVEL C
Very limited populations
evaluated*
Only consensus opinion
of experts, case studies, or
standards of care
▪Evidence from single
randomized trial or
nonrandomized studies
▪Recommendation that
procedure or treatment
is useful/effective
▪Some conflicting evidence
from single randomized trial
or nonrandomized studies
▪Recommendation in favor of
treatment or procedure being
useful/effective
▪Only expert opinion,
case studies, or standard
of care
Suggested phrases
should
for writing
is recommended
recommendations:
is indication
is useful/effective/
beneficial
Comparative effectiveness treatment/strategy
phrases†:
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
▪Recommendation in favor of
treatment or procedure being
useful/effective
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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