The text of the review should be succinct and readable. Although there is no formal word limit for Cochrane reviews, review authors should consider 10,000 words an absolute maximum unless there is special reason to write a longer review. Most reviews should be substantially shorter than this. A review should be written so that someone who is not an expert in the area can understand it, in light of the following policy statement, stated in the Cochrane Manual (The Cochrane Collaboration 2007):
“Cochrane reviews should be written so that they are easy to read and understand by someone with a basic sense of the topic who may not necessarily be an expert in the area. Some explanation of terms and concepts is likely to be helpful, and perhaps even essential. However, too much explanation can detract from the readability of a review. Simplicity and clarity are also vital to readability. The readability of Cochrane reviews should be comparable to that of a well written article in a general medical journal.”
The text of a Cochrane review contains a number of fixed headings that are embedded in RevMan. Subheadings may be added by the author at any point. Certain specific subheadings are recommended for use by all authors, but are not mandatory and should be avoided if they make individual sections needlessly short. Further subheadings that may or may not be relevant to a particular review are also discussed below.
Some headings are followed by fixed subheadings and therefore have no free text immediately following them: ‘Methods’, ‘Criteria for including studies’, ‘Results’, and ‘Authors’ conclusions’.
Background
[fixed, level 1 heading]
Well-formulated review questions occur in the context of an already-formed body of knowledge. The background should address this context, help set the rationale for the review, and explain why the questions being asked are important. It should be concise (generally around one page when printed) and be understandable to the users of the methodology under investigation. All sources of information should be cited.
Description of the problem or issue
[recommended, level 2 heading]
The review should begin with a brief description of the methodology being investigated and its significance. It may include information about how common the methodology is in evaluations of health care.
Description of the methods being investigated
[recommended, level 2 heading]
A description of the methods being investigated should place it in the context of any standard, or alternative methods in common use.
How these methods might work
[recommended, level 2 heading]
This section might describe the theoretical reasoning why the methods under review may have an impact in evaluations of health care. Authors may refer to a body of empirical evidence such as similar methods having an impact or identical methods having an impact in other settings. Authors may also refer to a body of literature that justifies the possible impact of the methods.
Why it is important to do this review
[recommended, level 2 heading]
The background should clearly state the rationale for the review and should explain why the questions being asked are important. It might also mention why this review was undertaken and how it might relate to a wider review of a general problem. If this version of the review is an update of an earlier one, it is helpful to state this by writing, for example “This is an update of a Cochrane review first published in YEAR, and previously updated in YEAR”. This may be supplemented with a brief description of the main findings of the earlier versions, with a statement of any specific reasons there may be for updating the review.
Objectives
[fixed, level 1 heading]
This should begin with a precise statement of the primary objective of the review, ideally in a single sentence. This might be followed by a series of specific objectives relating to different types of healthcare evaluation or different settings.
Methods
[fixed, level 1 heading]
The Methods section in a protocol should be written in the future tense. Because Cochrane reviews are updated as new evidence accumulates, methods outlined in the protocol should generally be written as if a suitably large number of studies will be identified to allow the objectives to be met (even if it is known this is not the case at the time of writing).
The Methods section in a review should be written in the past tense, and should describe what was done to obtain the results and conclusions of the current review. Often a review is unable to implement all of the methods outlined in the protocol, usually because there is insufficient evidence. In such circumstances, it is recommended that the methods that were not implemented be outlined in the section headed ‘Differences between protocol and review’ (see below), so that it serves as a protocol for future updates of the review.
Criteria for considering studies for this review
[fixed, level 2 heading]
Types of studies
[fixed, level 3 heading]
Eligible study designs should be stated here, along with any thresholds for inclusion based on the conduct of the studies or their risk of bias. For example, ‘All randomized controlled comparisons of different methods’ or ‘All cohorts of clinical trials with prospective registration of the trials’.
Types of data
[fixed, level 3 heading]
The raw material for the methodology studies to be included in the review should be described here, including any restrictions on, for example, the characteristics of the raw material (such as limiting to randomised clinical trials only). Examples of ‘Types of data’ in Cochrane Methodology reviews are “healthcare trials, including trials of clinical interventions and non-clinical interventions where the effects of the intervention on one or more health outcomes were measured” and “biomedical sciences research studies”. Subgroup analyses should not be listed here (see ‘Subgroup analysis and investigation of heterogeneity’ under ‘Methods’).
Types of methods
[fixed, level 3 heading]
The methods under investigation should be defined here, under separate subheadings if appropriate. It should be made clear which comparisons are of interest. An example of ‘Types of methods’ for a Cochrane Methodology review is “randomised trials with adequately versus inadequately concealed allocation”. Subgroup analyses should not be listed here (see ‘Subgroup analysis and investigation of heterogeneity’ under ‘Methods’).
Types of outcome measures
[fixed, level 3 heading]
Note that outcome measures do not always form part of the criteria for including studies in a review. If they do not, then this should be made clear. Outcome measures of interest should be listed in this section whether or not they form part of the inclusion criteria. Examples of ‘Types of outcome measures’ in Cochrane Methodology reviews are “the magnitude and direction of estimates of effect (e.g. relative risk reductions, odds ratios, standardised effect sizes) and imbalances in prognostic factors” and “subsequent full publication of the results described in the abstract and the time interval between presentation at meetings and subsequent publication”.
Primary outcomes
[recommended, level 4 heading]
Primary outcomes should be as few as possible. It is normally expected that the review should be able to analyse these outcomes if eligible studies are identified, and that the conclusions of the review will be based in large part on the findings of the review for these outcomes.
Secondary outcomes
[recommended, level 4 heading]
Non-primary outcomes should be listed here. The total number of outcomes addressed should be kept as small as possible.
Search methods for identification of studies
[fixed, level 2 heading]
The methods used to identify studies should be summarized. The following headings are recommended. Before starting to develop this section, authors should contact the Cochrane Methodology Review Group for guidance.
See also
Electronic searches
[recommended, level 3 heading]
The bibliographic databases searched, the dates and periods searched and any constraints, such as language should be stated. The full search strategies for each database should be listed in an appendix to the review. If the Cochrane Methodology Register (CMR) is searched for the review, a standard description of this register can be referred to but information should be included on when and how the CMR was most recently searched for the current version of the review and the search terms used should be listed.
See also
Searching other resources
[recommended, level 3 heading]
List grey literature sources, such as internal reports and conference proceedings. If journals are specifically handsearched for the review, this should be noted but handsearching done by the authors to help build the Cochrane Methodology Register should not be listed because this is covered in the standardized description of the Register. List people (e.g. researchers or topic specialists) and organizations who were contacted. List any other sources used, which may include, for example, reference lists, the World Wide Web or personal collections of articles. The following optional headings may be used, either in place of ‘Searching other resources’ (in which case they would be level 3 headings) or as subheadings (level 4).
Grey literature
Handsearching
Reference lists
Correspondence
See also
Data collection and analysis
[fixed, level 2 heading]
This should describe the methods for data collection and analysis.
Selection of studies
[recommended, level 3 heading]
The method used to apply the selection criteria. Whether they are applied independently by more than one author should be stated, along with how any disagreements are resolved.
See also
Data extraction and management
[recommended, level 3 heading]
The method used to extract or obtain data from published reports or from the original researchers (for example, using a data extraction/data collection form). Whether data are extracted independently by more than one author should be stated, along with how any disagreements are resolved. If relevant, methods for processing data in preparation for analysis should be described.
See also
Data collection is discussed in Chapter 7, including which data to collect (Section 7.3), sources of data (Section 7.4), data collection forms (Section 7.5) and extracting data from reports (Section 7.6)
Assessment of risk of bias in included studies
[recommended, level 3 heading]
The method used to assess risk of bias (or methodological quality). Whether methods are applied independently by more than one author should be stated, along with how any disagreements are resolved. The tool(s) used should be described or referenced, with an indication of how the results are incorporated into the interpretation of the results.
Measures of the effect of methods
[recommended, level 3 heading]
The effect measures of choice should be stated. For example, odds ratio (OR), risk ratio (RR) or risk difference (RD) for dichotomous data; difference in means (MD) or standardized difference in means (SMD) for continuous data. The following optional headings may be used, either in place of ‘Measures of treatment effect’ (in which case they would be level 3 headings) or as subheadings (level 4):
Dichotomous data
Continuous data
Time-to-event data
Unit of analysis issues
[recommended, level 3 heading]
Special issues in the analysis of studies with non-standard designs, such as cross-over trials and cluster-randomized trials, should be described.
See also
Unit of analysis issues are discussed in Chapter 9 (Section 9.3).
Methods for cross-over trials, cluster-randomized trials and other non-standard designs are discussed in Chapter 16.
Dealing with missing data
[recommended, level 3 heading]
Strategies for dealing with missing data should be described. This will principally include missing information for methodology studies (for example the loss of trials from cohorts of trials), and missing statistics (such as standard deviations or correlation coefficients).
See also
Assessment of heterogeneity
[recommended, level 3 heading]
Approaches to addressing design heterogeneity among the methodology studies should be described, along with how the authors will determine whether a meta-analysis is considered appropriate. Methods for identifying statistical heterogeneity should be stated (for example, visually, using a chi-squared test, or using I2).
See also
Assessment of reporting biases
[recommended, level 3 heading]
How publication bias, and other reporting biases are addressed (for example, funnel plots, statistical tests, imputation). Authors should remember that asymmetric funnel plots are not necessarily caused by publication bias (and that publication bias does not necessarily cause asymmetry in a funnel plot).
See also
Reporting biases are discussed in Chapter 10.
Data synthesis
[recommended, level 3 heading]
The choice of meta-analysis method should be stated, including whether a fixed-effect or a random-effects model is used. If meta-analyses are not undertaken, systematic approaches to synthesizing the findings of multiple studies should be described.
See also
Subgroup analysis and investigation of heterogeneity
[recommended, level 3 heading]
All planned subgroup analyses should be listed (or independent variables for meta-regression). Any other methods for investigating heterogeneity of effects should be described.
See also
Sensitivity analysis
[recommended, level 3 heading]
This should describe analyses aimed at determining whether conclusions are robust to decisions made during the review process, such as inclusion/exclusion of particular studies from a meta-analysis, imputing missing data or choice of a method for analysis.
See also
The following optional (level 3) heading for the Methods section may be helpful:
Methods for future updates
See also
Issues in updating reviews are discussed in Chapter 3.
Results
[fixed, level 1 heading]
Description of studies
[fixed, level 2 heading]
Results of the search
[recommended, level 3 heading]
The results sections should start with a summary of the results of the search (for example, how many references were retrieved by the electronic searches).
See also
Included studies
[recommended, level 3 heading]
It is essential that the number of included studies is clearly stated. This section should comprise a succinct summary of the information contained in the ‘Characteristics of included studies’ table. An explicit reference to this table should be included. Key characteristics of the included studies should be described, including the methods, data (e.g. type of clinical trial in methodology study), comparisons and outcome measures in the included studies and any important differences among the studies. Authors should note any other characteristics of the studies that they regard as important for readers of the review to know. The following optional (level 4) subheadings may be helpful:
Design
Sample sizes
Setting
Methods
Outcomes
Excluded studies
[recommended, level 3 heading]
This should refer to the information contained in the ‘Characteristics of excluded studies’ table. An explicit reference to this table should be included. A succinct summary of why studies were excluded from the review should be provided.
The following optional (level 3) headings may be used in the ‘Description of studies’ section:
Ongoing studies
Studies awaiting classification
New studies found at this update
Risk of bias in included studies
[fixed, level 2 heading]
This should summarize the general risk of bias in results of the included studies, its variability across studies and any important flaws in individual studies. The criteria that were used to assess the risk of bias should be described or referenced under ‘Methods’ and not here. How each study was rated on each criterion should be reported in a ‘risk of bias’ table and not described in detail in the text, which should be a concise summary.
For large reviews, aspects of the risk of bias assessment may be summarized for the primary outcomes under the following headings.
Allocation
[recommended, level 3 heading]
A summary of how the methods being investigated were assigned in any comparative methodological studies in the review. Judgements concerning the risk of bias that may arise from this assignment should be summarized here.
Blinding
[recommended, level 3 heading]
A brief summary of who was blinded or masked during the conduct and analysis of the methodology studies should be reported here. Judgements concerning the risk of bias associated with blinding should be summarized here.
Follow up and exclusions
[recommended, level 3 heading]
The completeness of data should be summarized briefly here for each of the main outcomes.
Selective reporting
[recommended, level 3 heading]
Concerns over the selective availability of data should be summarized briefly here, including evidence of selective reporting of outcomes, subgroups or analyses.
Other potential sources of bias
[recommended, level 3 heading]
Any other potential concerns should be summarized here.
Effects of methods
[fixed, level 2 heading]
This should be a summary of the main findings on the effects of the methods studied in the review. The section should directly address the objectives of the review rather than list the findings of the included studies in turn. The results of individual studies, and any statistical summary of these, should be included in ‘Data and analysis’ tables. Outcomes should normally be addressed in the order in which they are listed under ‘Types of outcome measures’. Subheadings are encouraged if they make understanding easier (for example, for each different data, comparison or outcome measure if a review addresses more than one). Any sensitivity analyses that were undertaken should be reported. Authors should avoid making inferences in this section.
See also
Presentation of results is addressed in Chapter 11 (Section 11.7).
Interpretation of numerical results is discussed in Chapter 12 (Sections 12.4, 12.5 and 12.6).
Discussion
[fixed, level 1 heading]
A structured discussion can aid the consideration of the implications of the review (Docherty 1999).
See also
Interpretation of results is discussed in Chapter 12.
Summary of main results
[recommended, level 2 heading]
Summarize the main findings (without repeating the ‘Effects of methods’ section) and outstanding uncertainties, balancing important benefits against important harms. Refer explicitly to any ‘Summary of findings’ tables.
Overall completeness and applicability of evidence
[recommended, level 2 heading]
Describe the relevance of the evidence to the review question. This should lead to an overall judgement of the external validity of the review. Are the studies identified sufficient to address all of the objectives of the review? Have all relevant types of data, methods and outcomes been investigated? Comments on how the results of the review fit into the context of current practice might be included here, although authors should bear in mind that current practice might vary internationally.
Quality of the evidence
[recommended, level 2 heading]
Does the body of evidence identified allow a robust conclusion regarding the objective(s) of the review? Summarize the amount of evidence that has been included (numbers of studies), state key methodological limitations of the studies, and reiterate the consistency or inconsistency of their results. This should lead to an overall judgement of the internal validity of the results of the review.
Potential biases in the review process
[recommended, level 2 heading]
State the strengths and limitations of the review with regard to preventing bias. These may be factors within, or outside, the control of the review authors. The discussion might include the likelihood that all relevant studies were identified, whether all relevant data could be obtained, or whether the methods used (for example, searching, study selection, data extraction, analysis) could have introduced bias.
Agreements and disagreements with other studies or reviews
[recommended, level 2 heading]
Comments on how the included studies fit into the context of other evidence might be included here, stating clearly whether the other evidence was systematically reviewed.
Authors’ conclusions
[fixed, level 1 heading]
The primary purpose of the review should be to present information, rather than to offer advice. Conclusions of the authors are divided into two sections:
Implications for systematic reviews and evaluations of health care
[fixed, level 2 heading]
The implications for systematic reviews and other evaluations of health care should be as practical and unambiguous as possible. They should not go beyond the evidence that was reviewed and be justifiable by the data presented in the review. ‘No evidence of effect’ should not be confused with ‘evidence of no effect’.
Implications for methodological research
[fixed, level 2 heading]
This section of Cochrane Methodology reviews may used by people making decisions about future research, and authors should try to write something that will be useful for this purpose. As with the ‘Implications for practice’, the content should be based on the available evidence and should avoid the use of information that was not included or discussed within the review. In preparing this section, authors should consider the different aspects of research, perhaps using types of study, data, methods and outcome as a framework. Implications for how research might be done and reported should be distinguished from what future research should be done. For example, the need for randomized trials rather than other types of study, for better descriptions of studies in the particular topic of the review, or for the routine collection of specific outcomes, should be distinguished from the need for comparisons of specific types of method, or for research in specific settings.
It is important that this section is as clear and explicit as possible. General statements that contain little or no specific information, such as “Future research should be better conducted” or “More research is needed” are of little use to people making decisions, and should be avoided.
See also
Acknowledgements
[fixed, level 1 heading]
This section should be used to acknowledge any people or organizations that the authors wish to acknowledge including people who are not listed among the authors. This would include any previous authors of the Cochrane review or previous sources of support to the review, and might include the contributions of the editorial team of the Cochrane Methodology Review Group. Permission should be obtained from persons acknowledged.
Contributions of authors
[fixed, level 1 heading]
The contributions of the current co-authors should be described in this section. One author should be identified as the guarantor of the review. All authors should discuss and agree on their respective descriptions of contribution before the review is submitted for publication on the CDSR. When the review is updated, this section should be checked and revised as necessary to ensure that it is accurate and up to date.
The following potential contributions have been adapted from Yank et al. (Yank 1999). This is a suggested scheme and the section should describe what people did, rather than attempt to identify which of these categories someone’s contribution falls within. Ideally, the authors should describe their contribution in their own words:
Conceiving the review.
Designing the review.
Coordinating the review.
Data collection for the review.
Designing search strategies.
Undertaking searches.
Screening search results.
Organizing retrieval of papers.
Screening retrieved papers against inclusion criteria.
Appraising quality of papers.
Extracting data from papers.
Writing to authors of papers for additional information.
Providing additional data about papers.
Obtaining and screening data on unpublished studies.
Data management for the review.
Entering data into RevMan.
Analysis of data.
Interpretation of data.
Providing a methodological perspective.
Providing a clinical perspective.
Providing a policy perspective.
Providing a consumer perspective.
Writing the review.
Providing general advice on the review.
Securing funding for the review.
Performing previous work that was the foundation of the current review.
Declarations of interest
[fixed, level 1 heading]
Authors should report any present or past affiliations or other involvement in any organization or entity with an interest in the review that might lead to a real or perceived conflict of interest. Situations that might be perceived by others as being capable of influencing a review author’s judgements include personal, political, academic and other possible conflicts, as well as financial conflicts. Authors must state if they have been involved in a study included in the review.
See also
A summary of the Collaboration’s policy on conflicts of interest appears in Chapter 2 (Section 2.6).
Financial conflicts of interest cause the most concern, and should be avoided, but must be reported if there are any. Any secondary interest (such as personal conflicts) that might unduly influence judgements made in a review (concerning, for example, the inclusion or exclusion of studies, assessments of the validity of included studies or the interpretation of results) should be reported.
If there are no known conflicts of interest, this should be stated explicitly, for example, by writing ‘None known’.
Differences between protocol and review
[fixed, level 1 heading]
It is sometimes necessary to use different methods from those originally described in the protocol. This could be because:
methods for dealing with a particular issue had not been specified in the protocol;
methods in the protocol could not be applied (for example, due to insufficient data or a lack of information required to implement the methods); or
methods are changed because a preferable alternative is discovered.
Some changes of methods from protocol to review are acceptable, but must be fully described in this section. The section provides a summary of the main changes in methods for the review over time. It should be used for the following.
Point out any methods that were determined subsequent to the most recent published protocol (e.g. adding or changing outcomes; adding ‘Risk of bias’ or ‘Summary of findings’ tables).
Summarize methods from the protocol that could not be implemented in the current review (e.g. because no studies fell in a particular pre-defined subgroup).
Explain any changes in methods from the protocol to the review, state when they were made and provide the rationale for the changes. Such changes should not be driven by findings on the effects of the methods under investigation. Consider the potential effect on the review’s conclusions of any changes in methods, and consider sensitivity analyses to assess this.
Published notes
[fixed, level 1 heading]
Published notes will appear in the review in the CDSR. They may include editorial notes and comments from the Cochrane Methodology Review Group, for example where issues highlighted by editors or referees are believed worthy of publication alongside the review. The author or source of these comments should be specified (e.g. from an editor or a referee).
Published notes must be completed for all withdrawn protocols and reviews, giving the reason for withdrawal. Only basic citation information, sources of support and published notes are published for withdrawn protocols and reviews.