Incidence and Prevalence Flashcards
Counts
How many persons have the disease or condition
Ratios
Comparison of two quantities in which one value does not contain the other
Proportions
Tell us what fraction of the population is affected-Division of two related numbers (i.e. numerator is a subset of the denominator)
Rates
Inform how fast a disease is occurring in a population- Division of two numbers; time is used in the denominator
Prevalence
Number of affected persons with a given disease in the population at a specific time divided by the number of persons in the population at that time.
Proportion
Calculating Prevalence
people who ARE cases at a specified time / Number of persons in the population at that time
Point Prevalence
Prevalence at a given point of time
Period Prevalence
Prevalence over a specified period of time
How to measure period prevalence
- Follow individuals over a period of time to capture all cases of existing or new disease.
- At a single point in time, ask individuals about their experience over a period of time.
- For example, “In the last 2 years, have you had a urinary tract infection?”
Incidence
Number of new cases of a disease that occur during a specified period of time in a population at risk for developing the disease.
Useful in an unstable population
Cumulative Incidence
The accumulation of new cases in the total population at risk over a specified period of time.
Useful in a stable population
Calculating cumulative Incidence
people who became newly ill during time of interest / # of persons at risk during the time of interest
Calculating Incidence
people who became newly ill during time of interest / # of persons at risk during the time of interest OR Person time at risk
Person time
total amount of time the population is observed during “at risk” period; sum of all individuals follow-up time
