The background rate of a particular condition refers to how often it typically occurs in a particular population or in the population at large.
Deeper dive
Researchers use the background rate of certain conditions to look for adverse events linked to medical interventions, such as pharmaceuticals or surgeries, and determine whether they occur at a higher rate among patients receiving the intervention. For example, if researchers want to determine how much higher the risk for a blood clot is following a particular surgery, they have to first find out how many people in the general population experience a blood clot even if no one in the population has had that surgery. If the background rate is one blood clot per 1,000 people, and those who undergo a specific surgery experience blood clots at a rate of five per 1,000 people, then the researchers know there is a good chance the surgery is what is contributing to the blood clot.
The next step would be to see if those individuals had other underlying conditions that might predispose them to blood clots.