Table 2.
| Methodology | Moderate–Impact-Factor Group | High–Impact-Factor Group | ||||||
|---|---|---|---|---|---|---|---|---|
|
AJOG (n=56) |
BJOG (n=59) |
Obstet Gynecol (n=66) |
Total (n=181) |
JAMA (n=58) |
Lancet (n=69) |
NEJM (n=63) |
Total (n=190) |
|
| Level I | ||||||||
| RCT without placebo | 4 (7) | 6 (10) | 2 (3) | 12 (7) | 9 (16) | 8 (12) | 11(17) | 28 (15) |
| RCT with placebo | 2 (4) | 5 (8) | 3 (5) | 10 (6) | 8 (14) | 9 (13) | 21 (33) | 38 (20) |
| Controlled trial, other | 0 | 0 | 0 | 0 | 2 (3) | 0 | 1 (2) | 3 (2) |
| Level II | ||||||||
| Cohort study | 28 (50) | 18 (31) | 17 (26) | 63 (35) | 10 (17) | 11 (16) | 8 (13) | 29 (15) |
| Prospective | 17 (30) | 14 (24) | 10 (15) | 41 (23) | 8 (14) | 11 (16) | 8 (13) | 27 (14) |
| Retrospective | 11 (20) | 4 (7) | 7 (11) | 22 (12) | 2 (3) | 0 | 0 | 2 (1) |
| Case–control study | 5 (9) | 5 (8) | 4 (6) | 14 (8) | 0 | 1 (1) | 5 (8) | 6 (3) |
| Cross-sectional study | 8 (14) | 13 (22) | 23 (36) | 44 (24) | 17 (29) | 9 (13) | 5 (8) | 31 (16) |
| Survey | 1 (2) | 6 (10) | 9 (14) | 16 (9) | 7 (12) | 1 (1) | 1 (2) | 9 (5) |
| Database | 3 (5) | 3 (5) | 10 (15) | 16 (9) | 6 (10) | 5 (7) | 0 | 11 (6) |
| Diagnostic | 0 | 1 (2) | 1 (2) | 2 (1) | 0 | 0 | 1 (2) | 1 (1) |
| Other | 4 (7) | 3 (5) | 4 (6) | 11 (6) | 4 (7) | 3 (4) | 3 (5) | 10 (5) |
| Level III | ||||||||
| Case report | 0 | 6 (10) | 14 (21) | 20 (11) | 6 (10) | 17 (25) | 10 (16) | 33 (17) |
| Case series | 0 | 1 (2) | 1 (2) | 2 (1) | 1 (2) | 0 | 2 (3) | 3 (2) |
| Systematic reviews | 2 (4) | 5 (8) | 2 (3) | 9 (5) | 5 (9) | 10 (14) | 0 | 15 (8) |
| Meta-analysis | 2 (4) | 2 (3) | 1 (2) | 5 (3) | 5 (9) | 7 (10) | 0 | 12 (6) |
| Other | 7 (13) | 0 | 0 | 7 (4) | 0 | 4 (6) | 0 | 4 (2) |