Guide for Developing a Cochrane Protocol - Cochrane Public Health ...

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Cochrane Handbook – Chapter 10 Data synthesis The protocol should outline the procedures you intend to use to analyse and summarise the study results, including whether or not you intend to carry out meta-analyses. This section should contain a clear rationale for any choices, considering the potential impact of each choice on the outcomes of the review. Meta-analyses should only be undertaken if participants, interventions and comparisons are judged to be sufficiently similar to ensure an answer that is meaningful. It may be useful to organise this section by study type and/or by type of outcome data (e.g. continuous or binary). More specifically, if the intention is to carry out a quantitative analysis of results, you should outline in the protocol: • the software package that will be used to conduct the analyses (this should be RevMan and alternatives should be discussed with the CPHG); • how statistics describing the overall literature will be presented; • why a particular effect size metric is to be used; • if adjustments to effect sizes will be made for any reason; • techniques to be used to combine results of separate tests; • techniques to be used to assess and then analyse variability in findings across tests. As a default option, the CPHG recommend using the random-effects model to incorporate heterogeneity into your meta-analyses (as opposed to the fixed-effect model). The randomeffects model allows for a greater level of natural heterogeneity between studies, assuming that each study is estimating a unique ‘true’ effect applicable to the time, population and context in which the study was conducted. Fixed effects meta-analysis may be included in subsequent sensitivity analysis or when significant justification is provided in the protocol. For qualitative syntheses (with or without a meta analysis), you need to provide a rationale for how you intend to organise studies/findings to arrive at reasonable conclusions and present information in a useful way for end-users of the review. For example, you may like to synthesise studies grouped by the type of intervention, the length of the intervention, the type of outcome, or by study design. It may be difficult to identify what is most appropriate at protocol stage but we encourage you to report your anticipated approach or to identify the options for analysis and how the decision on synthesis structure will be reached. You must include information about how you will summarise the findings of the review. Use the five GRADE considerations (study limitations, consistency of effect, imprecision, indirectness and publication bias) to assess the quality of the body of evidence for each outcome, and to draw conclusions about the quality of the body of evidence within the text of the review. Note that this does not mean you have to provide a GRADE rating for the quality of the body of evidence (high, moderate, low, very low), however you must consider the five factors mentioned above in your review. Be sure to justify and document all assessments so that they can be included in your review. These factors must be addressed irrespective of whether your review will include a ‘Summary of Findings Table’ (SoFT). If you plan to include a formal SoFT in your review, you should include this information in this section of your protocol. It is good practice to list the Last updated: 24 November 2011 - 16 -
outcomes (up to seven) that you plan to include within the SoFT, as well as which comparisons and subgroups will be covered, if appropriate. A SoFT should include the number of participants and studies for each outcome, summarise the intervention effect and include a measure of the quality of the body of evidence addressing the considerations listed above. Subgroup analysis and investigation of heterogeneity In this section you should list your proposed sub-group analyses, selecting key factors that may differ between or within your included studies, and that you anticipate will be associated with differences in the effect observed, such as differences in the population, intervention or context of the studies. These should be restricted in number with a rationale provided for each. Issues of equity may be a key consideration. Include information about any formal statistical tests that will be used to compare subgroups, in the event that there are sufficient studies for this to be meaningful. It may be possible to undertake a meta-regression. Please note if this is an option for your review. Resources Cochrane Handbook – Chapter 9 Campbell and Cochrane Equity Methods Group Equity Checklist: http://equity.cochrane.org/sites/equity.cochrane.org/files/uploads/equitychecklist.pdf Sensitivity analysis You should document in this section under what circumstances a sensitivity analysis will be undertaken. Sensitivity analysis is often confused with subgroup analysis – although they are different. Sensitivity analysis is undertaken to identify whether review findings are dependent on the decisions made during the review process, such as about study inclusion/exclusion, the selection of data to analyse, the analysis methods used, imputed data, and the impact of studies at high risk of bias. Some examples of decisions that may indicate a need for sensitivity analysis are listed in The Cochrane Handbook (Chapter 9, section 9.7). Where it is known in advance that decisions have been made that may affect the results of the review, sensitivity analysis should be planned and noted in the protocol. During the course of the review, other study characteristics may also be identified for inclusion in the sensitivity analysis. This is acceptable and should be stated as a possibility in the protocol. Resources Cochrane Handbook – Chapter 9 Acknowledgements Acknowledge any individuals or organisations who may have made a sufficient contribution to developing the protocol, (e.g. secretarial support, protocol referees, review advisory group members) but are not included in the Contributions of Authors section. Please ensure you have obtained permission to name these people in the protocol, otherwise a general acknowledgment based on roles (‘our advisory group members’, ‘external peer referees of the protocol’). It is not necessary to acknowledge the support of specific people within the CPHG team who have helped Last updated: 24 November 2011 - 17 -
Page 1 and 2: The Cochrane Public Health Group Gu
Page 3 and 4: Getting started Now that your title
Page 5 and 6: interventions for enhancing access
Page 7 and 8: design due to ethical or other reas
Page 9 and 10: Chapter 21 in Cochrane Handbook on
Page 11 and 12: published elsewhere. These addition
Page 13 and 14: If you are including ITS studies we
Page 15: Handbook which outlines the options
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Page 21 and 22: Appendix 1 - Guidance for establish
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Page 49 and 50: Are the interventions to be exclude
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