Comparing one group with another, expresses differences in the risk of something happening. For example, in comparison with group A, people in group B have a relative risk of 3 of being ill (they are three times as likely to get ill). A relative risk above 1 means the risk is higher in the group of interest; a relative risk below 1 means the risk is lower.
Learn more about HIV, including who’s at risk, where to get tested, and how you can prevent it.