Flashcards in Cohort studies (Lecture 4) Deck (37)
Define a cohort study
observational studies that allow a researcher to be a passive observer of natural events occurring in a naturally exposed and unexposed groups
What is the group allocation of the cohort studies based on?
1. exposure status
2. group membership
When are cohort studies useful?
When studying a rare exposure
What are two other names for a cohort study?
Incidence studies and longitudinal studies
What two measures of association are typically used in a cohort study?
risk of the disease or the outcome and the risk ratio or the relative risk
What are the reasons to pick a cohort study?
-unable to randomize or force the group allocation
-exposure of interest is rare
-more interested in the incidence or risk rates
What are the 3 ways in which a cohort study can be conducted in?
Define a prospective cohort study
exposure group is selected on the bases of past or current exposure and both groups are following into the future to assess for the outcomes
Define a Retrospective cohort study
At the start of the study, the exposure and the source has already occurred bit the groups are still allocated based on the past history of the exposure
What is another word for a retrospective study?
Where do you start at in a retrospective study?
At the time of exposure (historically- it is in the past) and then you follow it forward to the point of outcome that is in the present
*exposure has to occur before the outcome of interest and the group allocation is based on exposure status, not the disease status
Define an ambidirectional cohort study
Uses retrospective design to assess past differences but also adds future data collected on additional outcomes prospectively from the start of the study
How is an ambidirectional study considered to be bidirectional?
Looking for outcomes that are in the past and that are known in the present but also looks into the future
reders to a group with something in common
Define birth cohort
individuals that are grouped together based on being born in a geographic region in a given time period
Define inception cohort
Individuals that are grouped together at a given point based on a common factor
-where people live, where they work, something they have in common
Define exposure cohort
Individuals are assembled together based on a common exposure
True or false
Cohort changes cannot change over time
False: they may or may not change over time
Define a fixed cohort
a cohort which cannot gain members but can have loss to follow ups
Define a closed cohort
A fixed cohort with no loss to f/u
Define an open (dynamic) cohort
A cohort with new additions and some loss to f/u
How do you select the exposed study populations?
You allocate the subjects based on a predefined criteria of exposure
What are the goals of an unexposed study population?
To make the groups as close as possible (coming from the same cohort while also being unexposed)
What are the 3 sources that an unexposed group can come from?
2. General population
3. Comparison cohort
Describe the internal source of unexposed selection
patients come from the same "cohort" but are unexposed
If there are levels of exposure, use the lease exposed group as a comparator
Describe the general population selection group for the unexposed study population
used if the internal source is not available
everyone is exposed; the exposure subjects came from the general population
Describe the comparison cohort source of an unexposed selection
This is the LEAST acceptable
attempts to match the groups as close as possible on personal characteristics
cannot control for the other potentially harmful exposures in the comparison cohort
What are the strengths of a cohort study?
1. Multiple outcomes
2. rare exposures
3. calculating risk and RR
4. ethical issues are limiting the interventional, can use cohort
5. long conduction/latent periods (retro)
6. "temporality" (prospective)
What are the weaknesses of a cohort study?
1. Cannot demonstrate causation
2. hard to control for other exposures if more than one plausible for being associated with an outcome
3. retrospective cannot control for other exposures or potential changes in amount of study exposure
4. not good for long induction /latent period (prospective; retrospective is better)
5. impacted by unassisted confounders
6. impacted by biases (selection and recall)
7. limited by available data (retrospective; less for prospective)