effect estimate with no measure of precision direction of effect with P value or statement of statistical significance only the direction of effect).Ĭalculate the effect estimate and measure of precision from the available statistics if possible ( Chapter 6). Within a study, the intervention effects may be incompletely reported (e.g. Incompletely reported outcome or effect estimate This circumstance may reflect the infancy of research in a particular area, or that the specified PICO for the synthesis aims to address a narrow question.īuild contingencies into the analysis plan to group one or more of the PICO elements at a broader level ( Chapter 2, Section 2.5.3). Meta-analysis is not possible with no studies, or only one study. Limited evidence for a pre-specified comparison However, meta-analysis methods should be considered in these circumstances, as they may provide important insights if undertaken and interpreted appropriately. Other commonly cited reasons for not using meta-analysis are because of too much clinical or methodological diversity, or statistical heterogeneity (Achana et al 2014). Legitimate reasons include limited evidence incompletely reported outcome/effect estimates, or different effect measures used across studies and bias in the evidence. Some common reasons why it may not be possible to undertake a meta-analysis are outlined in Table 12.1.a. However, there are circumstances where it may not be possible to undertake a meta-analysis and other statistical synthesis methods may be considered (McKenzie and Brennan 2014). Meta-analysis of effect estimates has many potential advantages (see Chapter 10 and Chapter 11). Available from 12.1 Why a meta-analysis of effect estimates may not be possible Cochrane Handbook for Systematic Reviews of Interventions version 6.3 (updated February 2022). In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Chapter 12: Synthesizing and presenting findings using other methods. Synthesis methods that involve vote counting based on statistical significance have serious limitations and are unacceptable.Ĭite this chapter as: McKenzie JE, Brennan SE. When writing the review, details of the synthesis methods should be described. Tabulation and visual display of the results should always be presented alongside any synthesis, and are especially important for transparent reporting in reviews without meta-analysis.Īlternative synthesis and visual display methods should be planned and specified in the protocol. These methods provide more limited information for healthcare decision making than meta-analysis, but may be superior to a narrative description where some results are privileged above others without appropriate justification. Meta-analysis of effect estimates has many advantages, but other synthesis methods may need to be considered in the circumstance where there is incompletely reported data in the primary studies.Īlternative synthesis methods differ in the completeness of the data they require, the hypotheses they address, and the conclusions and recommendations that can be drawn from their findings.
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