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General Practice Notebook
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forest plot

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In a forest plot, the results of component studies are shown as squares centred on the point estimate of the result of each study

  • a horizontal line runs through the square to show its confidence interval - the confidence interval represented is generally, but not always, a 95% confidence interval
    • shows the estimated effect of interest for each of the separate studies in the meta-analysis
  • in the centre of the confidence interval for each study is a square
    • size of the square corresponds to the size of the study and therefore the precision of the estimate
  • the diamond symbol is used to represent the overall estimate from the meta-analysis and its confidence interval
    • centre of the diamond represents the pooled point estimate, and its horizontal tips represent the confidence interval
  • significance is achieved at the set level if the diamond is clear of the 'line of no effect'
    • a vertical line, known as the 'line of no effect' - represents equal effectiveness of the treatments (for example, it would correspond to a value of zero for a difference in means, or unity if the effect of interest were the odds ratio)
    • if an individual study has a confidence interval that crosses the 'line of no effect' then the results of that particular study were not statistically significant (at the chosen confidence interval)
  • plot allows readers to see the information from the individual studies that went into the meta-analysis at a glance
    • provides a simple visual representation of the amount of variation between the results of the studies, as well as an estimate of the overall result of all the studies together
  • more information about the Forest plot click here

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