|Level I||High quality randomized trial or prospective study; testing of
previously developed diagnostic criteria on consecutive patients;
sensible costs and alternatives; values obtained from many studies
with multiway sensitivity analyses; systematic review of Level I
RCTs and Level I studies.
|Level II||Lesser quality RCT; prospective comparative study; retrospective
study; untreated controls from an RCT; lesser quality prospective
study; development of diagnostic criteria on consecutive patients;
sensible costs and alternatives; values obtained from limited studies; with multiway sensitivity analyses; systematic review of Level II studies or Level I studies with inconsistent results.
|Level III||Case control study (therapeutic and prognostic studies); retrospective comparative study; study of nonconsecutive patients
without consistently applied reference “gold” standard; analyses
based on limited alternatives and costs and poor estimates; systematic review of Level III studies.
|Level IV||Case series; case control study (diagnostic studies); poor reference
standard; analyses with no sensitivity analyses.
|Level V||Expert opinion.|