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Relative Risk Calculator

Calculate relative risk from event counts in exposed and unexposed groups.

Calculator

Enter counts from your 2×2 contingency table:

In SPSS: Analyze → Descriptive Statistics → Crosstabs. Put Group/Exposure in rows and Outcome in columns. Click Statistics → Risk to get RR directly. The 4 cells: a = Exposed & Outcome+ (top-left), b = Exposed & Outcome− (top-right), c = Unexposed & Outcome+ (bottom-left), d = Unexposed & Outcome− (bottom-right). RR is used for cohort studies and RCTs where you can directly measure risk.

Outcome + Outcome − Exposed / Group A Unexposed / Group B

Outcome + = the disease or event occurred. Outcome − = it did not occur. For a cohort study: Outcome+ = developed the disease during follow-up.

Exposed / Group A = the group with the risk factor or intervention. Unexposed / Group B = the comparison or control group. RR = risk in exposed ÷ risk in unexposed. RR > 1 means higher risk in the exposed group.

Required Terms Explained

Outcome + means the event occurred. Outcome - means the event did not occur. Exposed / Group A is the treatment or risk-factor group. Unexposed / Group B is the comparison group. The 95% CI shows the uncertainty around the relative risk; if it includes 1.0, the observed risk difference may be compatible with no true association.

About this method

Relative risk compares event probability between two groups. RR > 1 indicates higher risk in the exposed group, while RR < 1 indicates reduced risk.

Frequently Asked Questions

When should I use relative risk?

Use relative risk in cohort studies, randomized trials, and designs where event risk can be directly estimated.

What does RR = 0.70 mean?

It means the exposed or treatment group has 30% lower risk compared with the reference group.

Can I use RR for case-control studies?

Usually no. Case-control studies generally report odds ratios.