Flashcards in Cohort Study Deck (17)
What is a Cohort Study?
Observational study allowing researchers to be passive observer of natural events occurring in naturally-exposed and unexposed groups
Cohort study designs include ____, ___ and ___.
Prospective, retrospective and ambidirectional
Why choose a cohort study?
Unable to force group allocation (unethical)
Limited Resources (time, money, subjects)
Interested in incidence rates or risk for outcome of interest
Fixed cohort is when
Closed cohort is when
Open/Dynamic cohort is when
No members can be added but losses can occur
No additions, no losses
Open, losses and additions can occur anytime
Give some examples of Cohort.
Inception Cohort (COB)
Exposure Cohort (9/11)
Cohort studies can be designed to be divide groups based on
Or group membership for "commonality"
Exposure group is selected on the basis of a past or current exposure and both groups followed into the future to assess for outcome of interest. No outcome known.
This study CAN show causation if precisely controlled with a well done design.
At the start of the study, both exposure and outcome of interest have already occurred but groups still allocated based on past history of exposure. Outcome known.
Lack of control since it already occurred, therefore no way to explain causation.
Using retrospective design to assess past differences but also add future data collected on additional outcomes PROSPECTIVELY.
Ex: Conducted study on exposure of Vietnam War vets on H1. Use medical records of past but still continue to follow them present day and future.
Selecting the exposure group is easier for Cohort studies since you are selecting based on ____
Selecting the unexposed group is harder for Cohort Studies but can be allocated from 3 sources:
Strengths of Cohort Studies
Good for accessing multiple outcomes for one exposure
Good for Rare Exposures
Useful in calculating risk and risk ratios
Less expensive than interventional
When ethical issues limit use of interventional
Good for long induction/latent periods (retrospective)
Able to represent temporality
Weakness of Cohort Studies
(general but mostly retrospective)
Can't demonstrate causation (unless well controlled and design prospective type)
In retrospective type: hard to control for other exposures if more than one plausible for being associated with outcome
In retrospective type: can't control for other exposures or potential changes in amount of study exposure
Retrospective: An be impacted by unassessed confounders and biases
Retrospective: Limited Data
Prospective: Not good for long induction/latent periods
Strengths of Prospective Cohort Studies
Can obtain better data since we have control over specific data collection
Following up and tracking patients are easier
Good for temporarility
Look at multiple outcomes from a single exposure
Calculate incidence and incidence rate
Disadvantages of Prospective
Time, expense and lost-to-follow-ups
Not efficient for rare diseases
Not suited for long induction/latency conditions
Exposure may change over time
Strengths of Retrospective Cohort
Best for long induction/latency
Able to study rare exposures
Useful if data exists
Saves time and money to not conduct prospective