Incidence is useful in understanding how commonly a disease or problem occurs over a period of time, which can be used to estimate one's risk of getting the disease.
Prevalence is a more relevant measure than incidence when assessing the impact of a problem within a community and to assess the subsequent needs. Although data on prevalence are easier to collect than incidence data, prevalence should be used with caution in evaluating associations between variables. In studies of prevalence it is very difficult to distinguish the effects of factors affecting the occurrence of disease from the effects of factors that increase survival (or duration of the problem). This difficulty often leads to incorrect conclusions.