Cohort and Case-Control Flashcards
What is a hypothesis?
A statement that an underlying tendency of scientific interest takes a particular quantitative value
If p<0.05, then we can accept/reject the null hypothesis?
Reject
What are advantages of a cohort study?
Study exposures and personal characteristics that are not routinely collected
Obtain more detailed information about outcomes and exposures
Can collect additional data on potential confounding factors
Limitations of an external comparison in a cohort study?
Limited data available for reference population
Often no incidence data
Usually have to just use mortality data
Study and reference populations may not be compatible - selection bias eg healthy worker effect
Disadvantages of cohort studies?
Large and resource intensive
Take a long time
High number of losses to follow up - survivor bias
Not good for rare diseases - too few cases
Difficulty with confounding
Why are cohort studies better than case control?
Can study a range of different outcomes
Can study a rare exposure
Can establish that exposure(s) precede outcome(s)
What ratios are used for internal and external studies?
Internal - incidence rate ratio
External - SMR
How are case-control studies set up?
Identify a group who are already ill (cases) and compare them to a group of people who are healthy (control)
Look at the exposure status of the two group
How would you set up the table for a control study in order to calculate the results?
Exposed, unexposed down the side
Cases then controls across the top
(Alphabetical order)
Issues with case control studies?
Selection bias
Information bias
Confounding
What is selection bias?
Error due to systematic differences in the ways in which the two groups were collected
Give two types of selection bias
Healthy worker effect
Allocation bias
What is information bias?
Error due to mis classification if subjects in the group
What are two types of information bias?
Recall bias
Publication bias
