Table 2

Modified rating scheme and results for N = 168 articles

Classification

Definition

Grade

Results

Systematic Review

Documented extensive literature search; quantitative or qualitative summary

A

9

Narrative Review

Summary of field or problem by an expert citing references obtained in a non-systematic manner

B

49

RCT

Prospectively randomized at individual or group level

C

3

Observational Studies

Formal design, almost always a control group whether prospective or retrospective, and whether cross-section, panel, or case-control. Includes analysis of large dataset analysis.

D

29

Mathematical Models

Uses mathematical language to describe and predict biomedical and epidemiologic outcomes.

E

12

Case Reports or Series

Report of a (hopefully pertinent) case or series of cases, often with a perspective on the current state of affairs or the current literature

F

30

Diagnostic Test Studies

Studies of the laboratory or filed performance of a diagnostic test. Generally compare sensitivity and specificity to some gold standard

G

0

Evidence Based guidelines

Guidelines developed by bodies after review of the literature

H

9

Expert Opinion, Editorials & Commentaries

Opinion or "newsy" narratives

I

27

TOTAL

168

Aledort et al. BMC Public Health 2007 7:208   doi:10.1186/1471-2458-7-208