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Meta-analysis: risk difference

Next selectMeta-analysis
Next selectRisk difference


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 risk difference under the fixed effects model. Next the heterogeneity statistic is incorporated to calculate the summary risk difference 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: Risk difference - how to enter data

Required input

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

Meta-analysis: Risk difference - 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: Risk difference - results

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

The pooled risk difference with 95% CI is given both for the Fixed effects model and the Random effects model. If the value 0 is not within the 95% CI, then the risk difference 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.

Forest plot

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

Meta-analysis: Risk difference - Forest plot


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.