Expresses how frequently something (such as a cancer) occurs in a given population (such as the UK) over a given period of time (usually a year). For example, the UK has a population of about 60 million and each year in the UK about 270,000 people are diagnosed with cancer. To get the rate, the number of people diagnosed each year (270,000) is divided by the size of the population (60 million) and multiplied by 100,000. This gives us a crude rate of around 450 cancers per 100,000 population.