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Meta-analysis: relative risk

Next selectMeta-analysis
Next selectRelative risk


For a short overview of meta-analysis in MedCalc, see Meta-analysis: introduction.

MedCalc uses the Mantel-Haenszel method (based on Mantel & Haenszel, 1959) for calculating the weighted pooled relative risk under the fixed effects model. Next the heterogeneity statistic is incorporated to calculate the summary relative risk under the random effects model (DerSimonian & Laird, 1986).

How to enter data

The data of different studies can be entered as follows in the spreadsheet:

Meta-analysis: relative risk - how to enter data

Required input

The dialog box for "Meta-analysis: relative risk" can then be completed as follows:

Meta-analysis: relative risk - dialog box

Studies: a variable containing an identification of the different studies.

Intervention groups

Control groups

Filter: a filter to include only a selected subgroup of cases in the graph.



Meta-analysis: relative risk - results

The program lists the results of the individual studies: number of positive cases, total number of cases, and the relative risk with 95% CI.

The pooled relative risk with 95% CI is given both for the Fixed effects model and the Random effects model. If the value 1 is not within the 95% CI, then the relative risk is statistically significant at the 5% level (P<0.05).

The random effects model will tend to give a more conservative estimate (i.e. with wider confidence interval), but the results from the two models usually agree where there is no heterogeneity. See Meta-analysis: introduction for interpretation of the heterogeneity statistics Cochran's Q and I2. When heterogeneity is present the random effects model should be the preferred model.

See Meta-analysis: introduction for interpretation of the different publication bias tests.

Note that when a study reports no events (or all events) in both intervention and control groups the study provides no information about relative probability of the event and is automatically omitted from the meta-analysis (Higgins & Green, 2011).

Forest plot

The results of the different studies, with 95% CI, and the overall effect with 95% CI are shown in a forest plot:

Meta-analysis: relative risk - forest plot

Note that the relative risks with 95% CI are drawn on a logarithmic scale.


See also

Recommended book

Book cover

Introduction to Meta-Analysis
Michael Borenstein, Larry V. Hedges, Julian P. T. Higgins, Hannah R. Rothstein

Buy from Amazon

This book provides a clear and thorough introduction to meta-analysis, the process of synthesizing data from a series of separate studies. Meta-analysis has become a critically important tool in fields as diverse as medicine, pharmacology, epidemiology, education, psychology, business, and ecology.