Table 2

Characteristics of the systematic reviews analysed

ALLAnswerNo answerp Value
NPer centNPer centNPer cent
Number of systematic reviews11810080683832
Number of co-authors0.240
 Median (IQR)6 (5–9)6 (4–7.5)6 (5–9)
Country of affiliation of 1st author0.969
 USA423627341539
 UK23191620718
 Canada21181418718
 Australia433413
 Others28242025821
Protocol registration/accessibility0.513
 No mention of protocol826953662976
 Protocol exists/not freely accessible332313
 Protocol exists/freely accessible33282531821
Source of funding of systematic review0.420
 Not reported877913
 Reported that no funding was received24201519924
 Reported that funding was received with details867358732874
Conflicts of interests of systematic reviewers0.130
 Not reported000000
 Reported that there were none42363341924
 Reported and detailed in the published report615239492258
 Reported elsewhere (eg, online)1513810718
Number of databases searched0.637
 Median (IQR)4 (3–7)4 (3–7)4 (3–6)
Language limitations applied0.569
 None564735442155
 English only423630381232
 Limitations to other languages766813
 Not specified1311911411
Number of studies included0.804
 Median (IQR)28 (12–57)28 (12–59)34 (12–55)
Study designs examined0.312
 RCT only463932401437
 Cohort prospective only544513
 Diagnostic studies only545600
 Various designs625339492361
  • Answer: reviews in which extracted data were confirmed by reviewers. No answer: reviews in which extracted data were not confirmed by reviewers. p Value testing the null hypothesis of equal distribution between the reviews for which the author responded to our inquiries and those who did not. Statistical tests: χ2 test or Kruskal-Wallis equality of population rank tests, as appropriate.

  • RCT, randomised controlled trials.