Table 2 Ratio of relative effect measures from observational studies and relative effect measures from RCTs (e.g., RR_obs/RR_rct): (a) among 74 pairs of pooled estimates, (b) with only one endpoint per review included, and (c) with studies reported in multiple reviews excluded

Ratio > 1*^a

31/74

41.9

12/29

41.4

24/65

36.9

Ratio < 1*^b

42/74

56.8

17/29

58.6

40/65

61.5

Ratio = 1*

1/74

1.4

0/29

0.0

1/65

1.5

Extreme difference (ratio > 1.43)

12/74

16.2

5/29

17.2

8/65

12.3

Extreme difference (ratio < 0.7)

20/74

27.0

8/29

27.6

19/65

29.2

Absence of an extreme difference (0.7 ≤ ratio ≤ 1.43)

42/74

56.8

16/29

55.2

38/65

58.5