The number of new occurrences of a condition or disease in the general or a specified population at a given period of time. For instance, at birth 1 in 2,400 babies in the UK has cystic fibrosis.
Contrast this with prevalence, which is the number of people living with a particular diagnosis in a defined population during a given period of time. According to the Cystic Fibrosis Trust, there are about 8,500 people in the UK with cystic fibrosis out of the total population of about 61.4 million (in 2010). The prevalence is therefore about 1 in 7,223.
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