Overview
This lecture explains the purpose and structure of forest plots in systematic reviews and describes how to interpret and summarize study results using these plots.
Purpose of Forest Plots
- Forest plots visually summarize findings from multiple studies in a systematic review.
- They quickly display individual study results and the combined overall outcome.
Structure of a Forest Plot
- A vertical line, called the "line of no effect," divides the plot into two sections.
- One side shows studies favoring the newer drug; the other side shows studies favoring the standard drug.
- Studies further from the line indicate a bigger difference between the drugs; those closer show less difference.
- Studies with no difference are placed on the line of no effect.
Interpreting Study Results
- Each study is represented by a square; the position reflects its outcome.
- The size of the square shows the size of the study (larger studies have bigger squares).
- A horizontal line through each square shows the confidence interval (CI), indicating certainty of the results.
- Longer CIs mean more uncertainty; shorter CIs mean more precise results.
Combining Results: Meta-Analysis
- A meta-analysis summarizes and averages the study results, giving more weight to larger studies.
- The combined result offers a clearer answer about which drug is more effective, based on existing research.
Key Terms & Definitions
- Forest Plot — a visual summary of individual study results in a systematic review.
- Line of No Effect — the vertical line dividing studies favoring either drug or showing no effect.
- Confidence Interval (CI) — a range expressing the uncertainty around a study result.
- Meta-Analysis — statistical method to combine results from multiple studies, weighting larger studies more.
Action Items / Next Steps
- Practice interpreting forest plots in recent systematic reviews.
- Review meta-analysis calculation basics for deeper understanding.