Lecture 10 - Cohort Studies Flashcards
What type of study is a cohort study?
Analytic observational study
What is a cohort study?
Where a group of people are selected with and without exposure, you then follow them up to observe the outcome to see if the outcome occurs in the individuals
The exposure is not controlled, you only watch
If 8 puppies are observed over a few years, and they are given snacks (not by you) and you observe to see if they get canine diabetes:
What is the exposure?
What is the outcome?
Exposure = snacks
Outcome = =diabetes
What is meant by the exposure is not controlled in a cohort study?
The exposure is not assigned by you
The participants essentially chose wether they expose themselves (Natural development occurs)
How does a cohort study compare to a RCT study?
Cohort study, the exposure is not controlled (Natural development)
RCT, exposure is controlled, you randomly assign people to have the exposure or no exposure
How do RCTs reduce the affects of (measured and non measured) confounders?
The random assignment of people in exposure or non-exposure means that the proportion of these individuals with these confounders should be evenly distributed between the 2 groups
What type of confounding cannot be mitigated in Cohort studies?
Unmeasured confounding cannot be mitigated
What is the problem with cohort studies not being able to mitigated unmeasured confounding?
There will be a higher proportion of individuals with the unmeasured confounder in one of the 2 groups
This will exacerbate the findings of the other group
See page 9 of Cohort study lecture for example:
(More individuals with the confounder in non exposure, these people with the exposure are more likely to die anyway, this makes the new chemo seem more effective since more people in the radiotherapy section will die)
What are the 2 types of cohort study?
Prospective
Retrospective
What is a prospective cohort study?
You start the study at the beginning and you see the people develop the outcom in real time
What is a retrospective cohort study?
When you study a group and determine the exposure and event after the data collection
Data has already been gathered, you are looking back in time
What are the strengths of a cohort study?
Efficient when randomisation is not feasible
Demonstrates the temporality of association
Uses Real world evidence which is the opposite to RCT
If you have a drug (exposure) and death (event), what does a RCT assess of the drug, what does a cohort study asses of the drug?
RCT assess efficacy of the drug
Cohort study assess effectiveness of the drug
What are the limitations of cohort studies?
Losses to follow up (people drop out, get differential loss and survivor bias)
More prone to CONFOUNDING
Large sample size needed for rare event/outcome
Takes a long time
