Biostats Calculator

Features > Relative risk

A relative risk measures a difference in the probability of a certain outcome between two groups of people - those who were exposed to a risk factor or treatment and those who were not. A statistically significant relative risk indicates that the risk factor is associated with the outcome, and if exposure is randomized as part of a trial it can demonstrate causality.

After selecting Relative risk from the menu, simply enter the number of individuals with each outcome, for both the exposed and unexposed group. Biostats Calculator will calculate the difference between the proportions and perform a hypothesis test to determine whether it is statistically significant.

Biostats Calculator reports:

• The relative risk (the outcome probability for exposed individuals divided by the probability for unexposed individuals)
• Confidence intervals for the relative risk, at the 90%, 95% and 99% confidence levels
• The number needed to treat or number needed to harm
• The p value, indicating how likely it is that the observed difference would occur due to chance alone
• whether the result is significant at the 95% confidence level

Biostats Calculator can perform this test and 11 others from the convenience of your iPhone or iPod Touch. Buy it today!

Related tests

• Odds ratio - a preferred outcome measure for case-control studies
• Chi-square test and Fisher's exact test - detect a difference in proportions between any number of groups