Exam 2 : Lecture Cohorts Flashcards
What type of study is a cohort, interventional or observational?
Observational
Groups are put together in two ways:
Allocation based on exposure status
Membership (something in common)
Allocation via membership means?
Everybody that uses blue cross blue shield or other such groups
When is it useful to study using a cohort?
Rare exposure
What are cohort studies termed?
Incidence studies/follow-up/ longitudinal studies
Reasons to select a cohort design
Unable to force group allocation
Limited resources
Exposure is rare
More interested in incidence rate
How can a cohort study be conducted?
Prospective
Retrospective
Ambidirectional
Exposure group is selected on basis of a past or current exposure and both groups followed into future to assess for outcome of interest, then compared
Prospective
Group allocation is based on exposure status not disease status
Retrospective
Individuals assembled at a given point based on some common factor
Ex: where they live, work,
Inception cohort
Types of cohort
Birth
Inception
Exposure
Cohort size
Fixed
Closed
Open
A cohort which can’t gain members but can have loss-to follow ups
Fixed
A cohort with no loss-to-follow ups
Closed
A cohort with new additions and some loss-to follow ups
Open
Unexposed can come from 3 places
Internal -patients from same cohort General population -2nd choice Comparison cohort -least acceptable
Strengths of cohort study
Good for assessing multiple outcomes of ONE exposure
Useful when exposure are rare
Useful in calculating risk and RR
Less expensive than inter
Good when ethical issues limit use of interventional
Good for long induction/later periods (retro)
Able to represent Temporality (prospective)
Advantages of prosepective cohort
Obtain greater amount of study info
Follow up easier
Better at giving answer to temporality
May look at multiple outcomes form a single exposure
Can calculate incidence and incidence rate
Disadvantages of prospective cohort
Time,expense, lost to follow up
Not efficient for rare disease
Not suited for long induction
Exposure may change over time
What are two things found in cohort studies during loss to follow up?
Type II error
Loss to follow up may not be equal between groups
How is a cohort retrospective study better than a cohort prospective study?
Saves time and money
Able to study rare exposures
Disadvantages of retrospective cohort
Requires access to charts, databases, employment records
Key biases with cohort studies
Healthy worker
Selection bias
