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Incidence and prevalence

Incidence and prevalence

These two terms are used to describe the frequency of a condition in a population.

The incidence is the number of new cases per population in a given time period.

For example, if condition X has caused 40 new cases over the past 12 months per 1,000 of the population the annual incidence is 0.04 or 4%.

The prevalence is the total number of cases per population at a particular point in time. It can be divided into two types:
  • point prevalence = number of cases in a defined population / number of people in a defined population at the same time
  • period prevalence = number of identified cases during a specified period of time / total number of people in that population

For example, imagine a questionnaire is sent to 2,500 adults asking them how much they weigh. If from this sample population of 500 of the adults were obese then the prevalence of obesity would be 0.2 or 20%.

Relationship
  • prevalence = incidence * duration of condition
  • in chronic diseases the prevalence is much greater than the incidence
  • in acute diseases the prevalence and incidence are similar. For conditions such as the common cold the incidence may be greater than the prevalence
+PassMedicine Notes

These two terms are used to describe the frequency of a condition in a population.

The incidence is the number of new cases per population in a given time period.

For example, if condition X has caused 40 new cases over the past 12 months per 1,000 of the population the annual incidence is 0.04 or 4%.

The prevalence is the total number of cases per population at a particular point in time. It can be divided into two types:
  • point prevalence = number of cases in a defined population / number of people in a defined population at the same time
  • period prevalence = number of identified cases during a specified period of time / total number of people in that population

For example, imagine a questionnaire is sent to 2,500 adults asking them how much they weigh. If from this sample population of 500 of the adults were obese then the prevalence of obesity would be 0.2 or 20%.

Relationship
  • prevalence = incidence * duration of condition
  • in chronic diseases the prevalence is much greater than the incidence
  • in acute diseases the prevalence and incidence are similar. For conditions such as the common cold the incidence may be greater than the prevalence


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