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. |