Case control & Cohort studies Flashcards
Case control time frame
Retrospective
Case control selection
Based on whether or not they have the outcome of interest
usually a relatively rare outcome
Case control- Exposure (risk factor) status is explored to
establish whether the exposure is more common in the case or control
Determines whether an exposure is associated with an outcome
What statistic can be calculated in a case control study?
Odds ratio
Advantages of case control studies
Quick
Cheap
Good for investigating outbreaks of infectious disease
Good for rare diseases
Can investigate many exposures simultaneously
Disadvantages of case control studies
Problems with selection of controls Subject to recall bias Uncertainty of exposure-disease time relationship Poor for rare exposures Can't calculate incidence rate directly
What can’t you calculate directly from a case control study?
Incidence rate
Cohort time frame
Prospective
Cohort selection
based on exposure status
followed over time to allow frequency of occurrence of outcome of interest in exposed & non-exposed groups to be compared
What statistic can a cohort study produce?
Relative risk
Why is a cohort study more accurate?
Gathered in real time
Provides incidence
Advantages of a cohort study
Can look at multiple outcomes
Follow through natural history of disease
Good design to look at risks related to rare exposures
Incidence can be calculated
Can minimise bias in estimating exposure if prospective
Disadvantages of a cohort study
Inefficient for studying rare diseases Expensive Time consuming Loss to follow-up may introduce bias Health worker/ volunteer may affect generalisability
Relative risk from cohort
Incidence in exposed/ Incidence in non-exposed
