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About meta-analyses

A systematic review may sometimes include a meta-analysis, although it is not a requirement of a systematic review. A meta-analysis can also stand alone and not be a part of a wider systematic review. 

A meta-analysis is a statistical analysis that combines data from previous studies to calculate an overall result.

One way of accurately representing all the data is in the form of a forest plot. A forest plot is a way of combining results of multiple studies in order to show point estimates arising from different studies of the same condition or treatment.

It is comprised of a graphical representation and often also a table. The graphical display shows the mean value for each study and often with a confidence interval (the horizontal bars). Each mean is plotted relative to the vertical line of no difference.

The following is an example of the graphical representation of a forest plot.


Image: “File:The effect of zinc acetate lozenges on the duration of the common cold.svg” by Harri Hemilä is licensed under CC BY 3.0

Activity

Watch the following short video where a social health example is used to explain how to construct a forest plot graphic.

Forest Plots – Understanding a Meta-Analysis in 5 Minutes or Less (5:38 min) by The NCCMT (YouTube)

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