Table 1 PRISMA-P (Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols) 2015 checklist: recommended items to address in a systematic review protocol

  Identification

1a

Identify the report as a protocol of a systematic review

  Update

1b

If the protocol is for an update of a previous systematic review, identify as such

  Registration

2

If registered, provide the name of the registry (e.g., PROSPERO) and registration number in the Abstract

  Contact

3a

Provide name, institutional affiliation, and e-mail address of all protocol authors; provide the physical mailing address of the corresponding author

  Contributions

3b

Describe contributions of protocol authors and identify the guarantor of the review

  Amendments

4

If the protocol represents an amendment of a previously completed or published protocol, identify as such and list changes; otherwise, state plan for documenting important protocol amendments

  Sources

5a

Indicate sources of financial or other support for the review

  Sponsor

5b

Provide a name for the review funder and/or sponsor

  Role of sponsor/funder

5c

Describe roles of funder(s), sponsor(s), and/or institution(s), if any, in developing the protocol

  Rationale

6

Describe the rationale for the review in the context of what is already known

  Objectives

7

Provide an explicit statement of the question(s) the review will address concerning participants, interventions, comparators, and outcomes (PICO)

  Eligibility criteria

8

Specify the study characteristics (e.g., PICO, study design, setting, time frame) and report characteristics (e.g., years considered, language, publication status) to be used as criteria for eligibility for the review

  Information sources

9

Describe all intended information sources (e.g., electronic databases, contact with study authors, trial registers, or other grey literature sources) with planned dates of coverage

  Search strategy

10

The present draft of the search strategy to be used for at least one electronic database, including planned limits, such that it could be repeated

  Data management

11a

Describe the mechanism(s) that will be used to manage records and data throughout the review

  Selection process

11b

State the process that will be used for selecting studies (e.g., two independent reviewers) through each phase of the review (i.e., screening, eligibility, and inclusion in meta-analysis)

  Data collection process

11c

Describe the planned method of extracting data from reports (e.g., piloting forms, done independently, in duplicate), and processes for obtaining and confirming data from investigators

  Data items

12

List and define all variables for which data will be sought (e.g., PICO items, funding sources), any pre-planned data assumptions and simplifications

  Outcomes and prioritization

13

List and define all outcomes for which data will be sought, including prioritization of main and additional outcomes, with rationale

  Risk of bias in individual studies

14

Describe anticipated methods for assessing the risk of bias of individual studies, including whether this will be done at the outcome or study level, or both; state how this information will be used in data synthesis

  Synthesis

15a

Describe criteria under which study data will be quantitatively synthesized

15b

If data are appropriate for quantitative synthesis, describe planned summary measures, methods of handling data, and methods of combining data from studies, including any planned exploration of consistency (e.g., I ², Kendall’s tau)

15c

Describe any proposed additional analyses (e.g., sensitivity or subgroup analyses, meta-regression)

15d

If quantitative synthesis is not appropriate, describe the type of summary planned

  Meta-bias(es)

16

Specify any planned assessment of meta-bias(es) (e.g., publication bias across studies, selective reporting within studies)

  Confidence in cumulative evidence

17

Describe how the strength of the body of evidence will be assessed (e.g., GRADE)