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
evaluated
a
Data derived from
multiple randomized
clinical trials or meta-
analyses
▪Recommendation that
procedure or treatment
is useful/effective
▪Sufficient evidence
from multiple
randomized trials or
meta-analyses
▪Recommendation in favor
of treatment or procedure
being useful/effective
▪Some conflicting evidence
from multiple randomized
trials or meta-analyses
LEVEL B
Limited populations
evaluated
a
Data derived from a
single randomized trial
or nonrandomized
studies
▪Recommendation that
procedure or treatment
is useful/effective
▪Evidence from single
randomized trial or
nonrandomized studies
▪Recommendation in favor
of treatment or procedure
being useful/effective
▪Some conflicting evidence
from single randomized trial
or nonrandomized studies
LEVEL C
Very limited populations
evaluated
a
Only consensus opinion
of experts, case studies,
or standard of care
▪Recommendation that
procedure or treatment
is useful/effective
▪Only expert opinion,
case studies, or
standard of care
▪Recommendation in favor
of treatment or procedure
being useful/effective
▪Only diverging expert
opinion, case studies, or
standard of care
Suggested phrases
for writing
recommendations:
should
is recommended
is indicated
is useful/effective/
beneficial
is reasonable
can be useful/effective/
beneficial
is probably recommended or
indicated
Comparative effectiveness
phrases
b
:
treatment/strateg y
A is recommended/
indicated in preference
to treatment B
treatment A should be
chosen over treatment B
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. Even when randomized trials are unavailable, there may be a very clear clinical
consensus that a particular test or therapy is useful or effective.
Estimate
of
Certainty
(Precision)
of
Treatment
Effect
Applying Classification of Recommendations and
Level of Evidence
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