EPI 1 Flashcards
What is a fixed population?
Permanent membership
– Membership is defined by an event, i.e. National Reserves
dispatched to Hurricane Katrina relief efforts
– Members cannot enter but they can leave (e.g., atomic bomb survivors)
What is a fixed and closed population?
Permanent membership
– Church picnic
– Members do not leave or enter. No losses occur (bad potato salad)
What is a dynamic or open population?
– Transient membership
– Defined by being in or out of a “state,” i.e. the population of a
given city
What are counts?
Counts tell us the number of people with a disease
What are proportions?
Proportions tell us what fraction of the population
is affected
What are rates?
Rates tell us how fast the disease is occurring in a
population
What are odds?
dds convey the possibility of the disease occurring
What are ratios?
Ratios give us information about what groups are at
higher risk of disease than others
What are proportions typically used for in EPI?
- Point and period prevalence and cumulative incidence
What is cumulative incidence?
Number of new cases that develop in a population at risk during a specified time period
Population at risk
– Susceptible population
– Must be free of disease at the beginning of the follow-up period
– Must have relevant organs
What is the formula for cumulative incidence?
Over a specified period of time
What needs to be in place for cumulative incidence?
– Population must be fixed
– Entire population is followed for the entire follow-
up period
– All first events are detected
What are other cumulative incidence measures?
Attack rate
Case fatality rate
What is the formula for attack rate?
What is the formula for case fatality rate?
What is prevalence?
Proportion of population who are existing cases (of
disease/event) at a given point or period of time
What is point prevalence?
proportion of population who are existing
cases at a given point in time (t)
What is period prevalence?
proportion of population who are existing
cases during a period of time
What is the formula for prevalence?
What type of measure would you use for a dynamic population?
Rate
What is incidence rate?
When would you use incidence rate?
Dynamic population
* Length of follow-up not uniform – not everyone is followed
for the entire time period
What are other names for cumulative incidence?
Attack rate
Risk
Incidence proportion
What are odds?
probability of event / probability of non-event
What is risk ratio?
What is the interpretation of risk ratio?
Individuals in the exposed group experienced X times the risk of
disease compared to individuals in the unexposed group
What is incidence rate ratio?
What is the interpretation of incidence rate ratio?
Individuals in the exposed group experienced X times the rate of
disease compared to individuals in the unexposed group
What is odds ratio?
What is the interpretation of odds ratio?
Individuals in the exposed group experienced X times the odds of
disease compared to individuals in the unexposed group
What is risk difference?
What is the interpretation of risk difference?
There is a _____ excess risk of outcome due to exposure.
What is the relationship between incidence and prevalence?
What factors increase disease prevalence?
Long Duration
– Low cure rate
– Low case fatality
* Increase in New Cases
* Improved Detection
* Immigration of Patients
* Emigration of Healthy People
What are factors that decrease prevalence?
- Short Duration
- Decrease in new cases
- Improved cure rate
- Emigration of patients
- Immigration of healthy people
What is the formula for mortality rate?
What are all the ratio formulas?
