Table 4.

Overlap between primary studies included in reviews

Number of times each study includeda	Total	Citation for studies
Included in 1 review	22	[24,25,41-60]
Included in 2 reviews	4	[39,61-63]
Included in 3 reviews	0
Included in 4 reviews	0
Included in 5 reviews	2	[26,35]
Total studies included in any review	28b

^aThe unit of analysis is the study (not publication). Where a study has multiple publications and review authors have included at least one of the publications, we have judged this study to be ‘included’ (Table 3).

^bThis table is based on 28 primary studies, including the two without an available abstract.