Frequently asked questions

What is a risk ratio (RR)?

The risk of an outcome in the treatment group divided by the risk in the control group. RR = 0.30 means the outcome occurred 30% as often with treatment—a 70% lower risk. RR = 1 means no difference; RR > 1 means treatment was associated with more of the outcome.

What is NNT / NNH?

Number Needed to Treat: how many patients must receive the treatment to prevent one additional bad outcome. Lower is better. Number Needed to Harm is the analogous figure for an adverse effect.

How do I read the forest plot?

Each row is one study. The square marks its risk ratio (larger squares carry more weight), and the horizontal line is the 95% confidence interval. The vertical line at 1 is “no effect”: markers and intervals entirely to its left favor treatment (green), entirely to its right favor control (red), and intervals crossing it are individually inconclusive (gray). The diamond at the bottom is the pooled random-effects estimate.

Why are some study numbers placeholders?

New topics may be seeded with illustrative counts to demonstrate the analysis before verified extractions are entered. Topic-specific caveats are noted on each topic page.

How do I add a topic or study?

Use the data-entry tool: enter a study's 2×2 table (or a reported effect), review the live-computed RR, CI, and NNT, then export a JSON file that drops straight into the site.