The patterns observed in descriptive epidemiology may suggest hypotheses about features associated with the cancer for testing by other means. Risk Risk is the probability or likelihood that a person will develop a disease. People sometimes talk about the probability of developing disease as 'absolute risk' but, in this volume, we use 'risk'. When describing risk of breast cancer or other disease in a population we use information from descriptive epidemiology about its frequency and distribution. The most useful measure of frequency is incidence or the number of new cases per 100,000 of the population per year.
Incidence is used as one measure of risk.
Risk can be expressed in a number of ways. If we say that 100 out of 100,000 Australian women each year will develop breast cancer then 100 per 100,000 per year is a measure of risk of breast cancer. These two measures are closely related. The first is a measure of risk over a short period of time while the second is an estimate of the cumulative risk over a long period. We have described the basic components of risk of breast cancer in Australian women, that is, the numbers of women diagnosed with breast cancer in a year or other specified time period within age groups, in Chapter 1.