Estimate of Certainty (precision) of Treatment Effect
Applying Classification of Recommendations and
Level of Evidencea
Size of Treatment Effect
CLASS I
CLASS IIa
Benefit >>> Risk
Benefit >> Risk
Procedure/Treatment Additional studies with
SHOULD be
focused objectives needed
performed/
IT IS REASONABLE
administered
to perform procedure/
administer treatment
LEVEL A
Multiple populations
evaluatedb
▪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
evaluatedb
▪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
evaluatedb
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 for
should
writing recommendations is recommended
is indicated
is useful/effective/
beneficial
Comparative effectiveness treatment/strategy
phrasesc
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.
a
This table, adopted in the 2012 focused update of the guideline, includes a newer classification
that is slightly different to that adopted in the 2007 guideline. As such, older recommendations
from the 2007 guideline that were class III were not classified into Class III: No Benefit or
Class III: Harm (as is the case in newer recommendations included in the 2012 guideline).
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