Lecture 19 Cohort study Flashcards
cohort study
allows Analytic epidemiology
Observational
Analytic epidemiology
- Examining observations between exposures and outcomes
- Causation
Observational
observe people’s exposures and what happens to them
what is a cohort study?
Individuals are defined based on the presence or absence of exposure to a suspected risk factor
Look at people who are exposed to potential risk factor follow over time to see if they develop the outcome interested in
cohort studies step by step use
GATE frame
- Identify a source population
- Recruit your sample population
* *Sample population must not already have the outcome of interest - Assess exposure to identify which group participants belong in (exposed or not exposed i.e. comparison)
- Follow up over time
- Observe whether or not participants develop the outcome
- Calculate measures of occurrence and measures of association
What can we measure using cohort studies?
Measures of occurrence
- Incidence proportion (IP)
- Incidence rate (IR)
measures of association
- RR
- RD
Incidence proportion
Proportion of people who develop the disease during a time period
Specify time period
Incidence proportion calculation
of people who develop disease in a specific period / # of people at risk of developing disease at start of period
Incidence rate
Accounting for different lengths of time that people may be in the study
Measure of the rate of onset of the disease
Incidence rate calculation
of people who develop disease in a specific period / # of person years at risk of developing disease
Relative risk
Number of times is likely it is that the exposed grouped will develop the disease compared with the comparison group
Risk difference
Number of extra cases of that outcome there were in the exposed group compared to the comparison group
How many fewer cases there were
RR calculation
I exposed / I comparison
RD calculation
I exposed - I comparison
Recruit your sample population for cohort study
- Randomly selecting a single group of participants
- completely separate to whether the participants have the exposure or not (some will have exposure and some may not they will be classified accordingly)
- Sometimes study a rare exposure that generally appears in a particular group of people