Lecture 10 Flashcards
What are the reasons to use a cohort study?
Unable to randomize
Limited resources
More interested in incidence rates/predictors than effects of interventions
Cohort Study Design
Observational & analytical studies allowing passive observance of natural events occurring in naturally-exposed and unexposed groups
*Always start knowing the exposure/disease
T/F: A cohort is a group with something in common.
True
Birth Cohort
People grouped based on being born in a certain region/time period (KC in 2000)
Inception Cohort
People grouped at a given point based on some common factor (where they live, work, etc.)
What is the most popular inception cohort in the U.S.?
Framingham Study…followed population of Framingham, MA starting in 1948 through today
Exposure Cohort
People grouped based on some common exposure
Fixed Cohort
Can’t gain members but can have loss-to-follow-ups
Closed Cohort
Fixed cohort with no loss-to-follow-ups
Open/Dynamic Cohort
Some new additions and loss-to-follow-ups
What are the 2 primary purposes of cohort studies?
Descriptive: measure of frequency (incidence/incidence rate)
Analytic: measures of association (risk ratio & predictive risk-factors)
Prospective Cohort Study
Exposure group selected on the basis of past or current exosure and both groups followed into future to assess outcome(s) of interest, then compare
Retrospective Cohort Study
At the start of the study, both the exposure and the outcome of interest have occurred
Ambidirectional Cohort Study
Uses retrospective design to assess past differences but ads all data collected on additional outcomes prospectively from start of study (looking for outcomes in both directions)
Advantages of Prospective Cohort Studies…
Obtain greater amount of important information from patients
Follow-up may be easier
Better at giving answer to “temporality”
Look at multiple outcomes from single exposure
Calculate incidence/incidence rate
Disadvantages of Prospective Cohort Studies…
Time/expense/loss-to-follow-up’s
Not efficient for rare diseases
Not suited for long induction/latency conditions
Exposure may change over time
Advantages to Retrospective Cohort Studies…
Best for long induction/latency conditions
Able to study rare exposures
Useful if data already exists
Saves time and money
Disadvantages of Retrospective Cohort Studies…
Requires access to private charts, databases, & employment records
Information may not factor in other exposures
Patients may not be available to interview
Exposure may have changed over time
When selecting the unexposed group, where should they come from?
1) Internal
2) General Population
3) Comparison Cohort
What are the 2 key biases with cohort studies?
Healthy-worker effect: Only healthy people work, unhealthy ones don’t work
Selection bias: How exposure status is defined/determined
