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.