Cohort Studies Flashcards
What is a cohort study?
Identifying outcome free individuals
Group individuals according to exposure
Ascertain outcomes for everyone
Compare incidence rates for exposure groups
What is an ideal study and what is the problem with this?
Comparing like for like
Have 2 identical groups that only differ on exposure of interest
How do you get 2 identical groups??
Cofounding factors normally apparent
What is person years?
The sum of total time of everybody followed up in a study
How do you calculate incident rate ratios?
Calculate IR for each exposure group separately
Eg, cases smoker/person years smoker (do same for non smokers
Compare using IRR
What are advantages over routinely available data?
Can study exposures that aren’t routinely collected
Obtain more detailed info
Collect additional data on cofounding factors
What is concurrent/ prospective case control?
Prospective follow up
Data collected may start immediately or later
What is historical or retrospective cohort studies?
Collecting follow up data from the past
Data collection starts in the past
Why do we use a standardised mortality ratio?
Studies over long periods of time
People age
Disease rates of differing populations change
What are advantages of cohort studies?
Concurrent; detailed and prospective assessment of exposure, outcomes and cofounders
Over case-control; range outcomes
- rare exposures
- establishing that exposure predates outcome
Better for conditions that fluctuate with age
What are disadvantages of cohort studies?
Resource and time intensive
Rigorous definitions of exposures and outcomes needed
Risk number of losses to follow up (survivor bias)
Hard to deal with confounding factors
