Statistics and Data
Relative Risk Calculator
Relative Risk Calculator calculate exposed and unexposed risks, relative risk, risk difference, odds ratio, and number needed to treat or harm from a 2x2 table.
Statistics and Data
Relative Risk Calculator
Calculate exposed and unexposed risks, relative risk, risk difference, odds ratio, and number needed to treat or harm from a 2x2 table.
Formula
Relative risk = [a/(a+b)] / [c/(c+d)]; odds ratio = ad/bc.
About the Relative Risk Calculator
Calculate exposed and unexposed risks, relative risk, risk difference, odds ratio, and number needed to treat or harm from a 2x2 table.
How the Relative Risk Calculator Works
Event and nonevent counts are converted to group risks, then their ratio and difference are reported with the cross-product odds ratio.
Formula
Relative risk = [a/(a+b)] / [c/(c+d)]; odds ratio = ad/bc.
The calculation runs in your browser. Values are validated for required ranges, compatible units, and method-specific restrictions before results are displayed.
Required Inputs
- Exposed group events a (required).
- Exposed group nonevents b (required).
- Unexposed group events c (required).
- Unexposed group nonevents d (required).
Results Reported
The result panel reports the final answer and the intermediate quantities needed to check the calculation:
- Relative risk
- Risk in exposed group (%)
- Risk in unexposed group (%)
- Absolute risk difference (percentage points)
- Odds ratio
- Number needed to treat or harm
- Effect direction
Relative Risk Calculator Example
Select Example Data in the calculator to load this reproducible input set:
| Input | Example value |
|---|---|
| Exposed group events a | 30 |
| Exposed group nonevents b | 70 |
| Unexposed group events c | 15 |
| Unexposed group nonevents d | 85 |
How to Use the Calculator
- Confirm that the calculator title and formula match the quantity you need.
- Enter every required value using the unit shown with its field.
- Select Example Data to inspect a valid input set, or enter your own values and select Calculate.
- Review all reported values and the displayed formula before using the answer.
- Use Copy Result or Download CSV when you need a reusable record.
Accuracy and Limitations
Zero cells can make ratios undefined and observational association does not establish causation. Confidence intervals, confounding, matching, and study design require separate analysis.
Keep units consistent, use measurements that represent the actual situation, retain full precision during the calculation, and round only the final answer. Professional decisions may require current official rules, field measurements, laboratory methods, or specialist review.
Frequently Asked Questions
What does the Relative Risk Calculator calculate?
Calculate exposed and unexposed risks, relative risk, risk difference, odds ratio, and number needed to treat or harm from a 2x2 table.
Which formula does the Relative Risk Calculator use?
Relative risk = [a/(a+b)] / [c/(c+d)]; odds ratio = ad/bc. Event and nonevent counts are converted to group risks, then their ratio and difference are reported with the cross-product odds ratio.
What should I check before using the Relative Risk Calculator result?
Zero cells can make ratios undefined and observational association does not establish causation. Confidence intervals, confounding, matching, and study design require separate analysis.