If you have an exact title add ti= (eg. ti=Emergency Medicine)
Simply put, this stage involves combining and then evaluating the data that you have extracted from your included studies.
The methods used during this stage depend on whether you have extracted quantitative data, qualitative data, or both.
Framework for synthesis
Box 9.2.a of the Cochrane Handbook, linked below, outlines an overall framework for the process of synthesis.
Meta-analysis is a statistical procedure to combine results data from two or more studies.
Factors which may exclude meta-analysis
It is not always possible or appropriate to conduct a meta-analysis, for example:
For additional factors, see Chapter 12 of the Cochrane Handbook, Why a meta-analysis of effect estimates may not be possible.
Performing meta-analysis
There are a number of different statistical models and methods used in meta-analysis, which are discussed in the below chapters of the Cochrane Handbook and the JBI Manual for Evidence Synthesis.
Cochrane Handbook - Analysing data and undertaking meta-analyses
The Library has several books on meta-analysis, available either as eBooks or in hard copy. Click the images below to find a copy.
Recommended articles on meta-analysis
Software for meta-analysis
SPSS
SPSS (Statistical Package for the Social Sciences) is software used to analyse data and run statistical procedures. Monash Health employees and students can use SPSS on specific computers at our Clayton, Dandenong, and Casey libraries. Look for the computer with the SPSS sign or ask Library staff.
Meta-Essentials
A free meta-analysis tool created by researchers at the Erasmus Research Institute of Management. Meta-Essentials is a series of workbooks designed for Microsoft Excel which will produce statistics, tables, and figures when you enter data.
Click the link below to access the user guide, FAQ, and download Meta-Essentials.
Network meta-analysis
A network meta-analysis must be planned for at the outset of a review. The Cochrane Handbook recommends that the review team include a statistician with experience in network meta-analysis, and that they be involved early and for the duration of the review.
Cochrane Handbook - Undertaking network meta-analyses
More information
If a meta-analysis is not possible or appropriate, other methods of synthesis are available. See Chapter 12 of the Cochrane Handbook for more information.
Cochrane Handbook - Chapter 12, Section 12.2
Synthesis Without Meta-analysis (SWiM)
SWiM is an umbrella term which may refer to various methods of synthesising quantitative effect data in reviews of interventions. SWiM is not, in itself, a method of synthesis.
The SWiM Reporting Guideline details the aspects of synthesis which should be considered, documented, and ultimately reported on when the review is written up.
SWiM in systematic reviews: Reporting guideline
Cochrane offers a free online training module on using the SWiM reporting guidelines. To access it, you must first create a free Cochrane account.
The Cochrane Handbook (Section 12.2) cautions against narrative synthesis that lacks rigour and transparency. See the below guidance on narrative synthesis produced via the UK's Economic and Social Research Council (ESRC) Methods Programme.
Guidance on the Conduct of Narrative Synthesis in Systematic Reviews
Resources on narrative synthesis
Various methods can be used to synthesise and analyse qualitative data. Common methods include those listed in the table below.
| Method | Explanatory article |
|---|---|
| Qualitative metasummary | Using qualitative metasummary to synthesize qualitative and quantitative descriptive findings (2007) by M. Sandelowski et al. |
| Thematic synthesis | Methods for the thematic synthesis of qualitative research in systematic reviews (2008) by J. Thomas & A. Harden |
|
Framework synthesis |
“Best fit” framework synthesis: refining the method (2013) by C. Carroll et al. |
| Meta-ethnography |
Meta-ethnography in healthcare research: a guide to using a meta-ethnographic approach for literature synthesis (2021) by R. Sattar et al. |
| Meta-aggregation |
Qualitative research synthesis: methodological guidance for systematic reviewers utilizing meta-aggregation (2015) by C. Lockwood et al. |
For a more exhaustive list of available methods, see Table 1 on p. 16 of INTEGRATE-HTA's publication, Guidance on choosing qualitative evidence synthesis methods for use in health technology assessments of complex interventions by Booth et al.
Key guidance
Cochrane Handbook
Section 21.10, 'Selecting a qualitative evidence synthesis and data extraction method', includes a table of recommended methods -- thematic synthesis, framework synthesis, and meta-ethnography -- and their pros and cons.
Cochrane Handbook - Section 21.10
Cochrane-Campbell Handbook for Qualitative Evidence Synthesis
This new handbook, released in 2023, features chapters on framework synthesis and meta-ethnography. To access, visit the link below and create a free Cochrane account.
Cochrane-Campbell Handbook for Qualitative Evidence Synthesis
JBI Manual for Evidence Synthesis
JBI prefers a meta-aggregative approach, which "seeks to enable generalizable statements in the form of recommendations to guide practitioners and policy makers (Hannes and Lockwood 2011)". Meta-ethnography, narrative synthesis, and thematic synthesis are also briefly discussed.
The JBI approach to qualitative synthesis
More information
Software
NVivo software for qualitative data analysis is available on select PCs in Clayton, Dandenong, and Casey libraries -- look for the signed PC at each library.
After synthesis, you must assess the certainty of the evidence for each individual outcome in your review (per Item #15 frrom PRISMA).
How?
This process shares characteristics with the critical appraisal stage, but is a separate and more robust process which is used to rate the body of evidence at the outcome level rather than the study level. Best practice is to take a transparent and structured approach to assessment, e.g. using GRADE.
Review teams with 3 members or less can use the free version of GRADEpro GDT, an online tool, to conduct the assessment and generate a summary of findings (SoF) table. See the Reporting Findings page of this guide for more information on SoF tables.
Why?
Your certainty of evidence assessments will influence how readers -- such as clinicians and policy-makers -- apply the findings of your review to their own setting or clinical practice. It transforms your findings from evidence to recommendations (read more).
The GRADE approach
Grading of Recommendations Assessment, Development and Evaluation (GRADE) is the most common approach to assessing the certainty of evidence. It is considered a best practice approach by organisations responsible for producing clinical guidelines, such as the NHMRC and NICE.
The five GRADE considerations are:
Based on these considerations, GRADE categorises the certainty in a body of evidence as 'High’, ‘Moderate’, ‘Low’, or ‘Very low’.
See Chapter 14.2 of the Cochrane Handbook for more information about using GRADE.
Cochrane Handbook - Chapter 14.2
The GRADE Handbook provides detailed guidance on how to apply the GRADE approach.
Qualitative evidence - GRADE-CERqual
Use the GRADE-CERqual approach if you are conducting a qualitative or mixed-methods systematic review. GRADE-CERqual assessment is based on four components:
Click here to read example papers that have applied GRADE-CERqual.
The GRADE-CERqual Working Group has published a series of articles which provide in-depth guidance on how to apply GRADE-CERqual.
Article series - Applying GRADE-CERQual...
Alternatives to GRADE
GRADE is by far the most common and well-established method of assessing the certainty of evidence. Two alternatives are linked below.
Summary of findings table
The results of your assessment must be presented as part of a Summary of Findings table. Find more information on the Reporting Findings page of this guide.
The Monash Centre for Health Research and Implementation (MCHRI) offers clinical staff at Monash Health one free biostatistics consultation, a total of up to 2 hours of statistical support. Additional support is thereafter offered for a fee. See the link below for more information.
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