Table 2 The item-based comparison on the quality of registered (or with a prior protocol) DRMAs and matched controls

 Item 1: Was there duplicate study selection?

0.63

 Item 2: Was there duplicate data extraction?

0.01

 Item 3: Was there at least two database searched?

0.86

 Item 4: Was there any search strategy documented?

< 0.01

 Item 5: Was the status of publication used as an inclusion criterion?

0.25

 Item 6: Was a list of studies of included provided?

0.20

 Item 7: Was a list of studies of excluded provided?

0.02

 Item 8: Were the characteristics of the included studies provided?

0.59

 Item 9: Was the scientific quality of the included studies assessed?

0.46

 Item 10: Was the scientific quality of the included studies documented (only provide total score should be avoided)?

0.79

 Item 11: Was the scientific quality of the included studies used appropriately in formulating conclusions?

0.84

 Item 12: Were the methods used to combine the findings (dose-response) of studies appropriate?

0.66

 Item 13: Was the likelihood of publication bias assessed?

< 0.01

 Item 14: Was the conflict of interest stated?

0.14

 Item 1 (Title): Identify the report as a systematic review, meta-analysis, or both.

≈ 1

 Item 2 (Introduction): Describe the rationale for the review in the context of what is already known.

≈ 1

 Item 3 (Introduction): Provide an explicit objective(s) with reference to PICOS principle.

≈ 1

 Item 4 (Methods): Specify criteria for eligibility, giving rationale.

0.76

 Item 5 (Methods): Describe all information sources (e.g. databases) in the search and date last searched.

≈ 1

 Item 6 (Methods): Present full electronic search strategy for at least one database.

< 0.01

 Item 7 (Methods): State the process for selecting studies (two stage: title and abstract screen, then the full text).

0.23

 Item 8 (Methods): Describe method of data extraction and any processes for obtaining and confirming data.

0.12

 Item 9 (Methods): List and define all variables for which data were sought and any assumptions made.

≈ 1

 Item 10 (Methods): Describe methods used for assessing risk of bias of individual studies.

0.62

 Item 11 (Methods): State the principal summary measures (e.g., risk ratio, difference in means).

0.14

 Item 12 (Methods): Describe the methods of handling data and combining results of studies.

≈ 1

 Item 13 (Methods): Specify any assessment of risk of bias for the pooled evidence (e.g. publication bias).

0.02

 Item 14 (Methods): Describe methods of additional analyses (e.g. sensitivity analysis, meta-regression).

0.11

 Item 15 (Results): Give numbers of studies screened, assessed for eligibility, and included in the review, with reasons for exclusions at each stage, ideally with a flow diagram.

0.83

 Item 16 (Results): For each study, present characteristics for which data were extracted.

0.42

 Item 17 (Results): Present data on risk of bias of within each study (study level).

0.90

 Item 18 (Results): Present summery data, effect estimates and confidence intervals for each study.

0.34

 Item 19 (Results): Present results of each meta-analysis, with confidence intervals and measures of consistency.

≈ 1

 Item 20 (Results): Present results of risk of bias across studies (publication bias, outcome level).

< 0.01

 Item 21 (Results): Give results of additional analyses, if done.

0.20

 Item 22 (Discussion): Summarize the main findings including the strength of evidence for each main outcome.

0.34

 Item 23 (Discussion): Discuss limitations at study and outcome level

0.03

 Item 24 (Discussion): Provide a general interpretation of the results and implications for future research.

≈ 1

 Item 25 (Funding): Describe sources of funding and other support for the systematic review.

< 0.01