Introduction Overview incidence and prevalence are methods of measuring disease frequency in a population with respect to time Incidence describes the amount of new disease cases in at-risk people over a certain time period at risk means those who are capable of developing the disease of interest do not already have the disease are not vaccinated against the disease have at-risk anatomy (patients without a prostate cannot get prostate cancer) incidence can be specified 2 ways # of new cases in a population/# of at risk people in the population per unit time login to view 1 more bullet # of new cases in a population/time spent at risk (person-time) login to view 3 more bullets Prevalence proportion of population that has a disease or risk factor at a specified point or period in time existing cases/total number of people in specific population at a particular time e.g., percent of the U.S. population with diabetes in 2018 indicates overall disease burden of population helpful for resource allocation prevalence = incidence x duration factors that increase prevalence include increase in new cases (increased incidence) improved quality of care → decreased mortality → longer duration improved diagnostic ability → higher incidence in-migration of cases or susceptible people out-migration of healthy people factors that decrease prevalence include high case-fatality rate → shorter duration (aggressive cancers) decrease in new cases (decreased incidence) login to view 4 more bullets