A set of training materials for professionals working in intervention epidemiology, public health microbiology and infection control and hospital hygiene.
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Many text books have described advantages and disadvantages of cohort and case control studies. The following table summarises useful comments.
Case control studies
Suited for rare diseases
Yes since starting with a set of cases
Suited for rare exposures
Yes since starting with exposure status
Allows for studying several exposures
Difficult but examples exists
Allows for studying several outcomes
Disease status easy to ascertain
Easier since starting point of the study
Exposure status easier to ascertain
Yes since starting point of the study.
Except for retrospective cohorts
Allows computation of risk and rates
Allows computation of effect
Computation of risk ratio
and rate ratio
Estimation of risk ratio, rate ratio
from odds ratio
Allows studying natural history of disease
Easier to show that cause precedes effect.
Temporality between cause and effect difficult to establish
Based on existing data sources
Yes but access to information sometimes difficult
Easiness to find a reference group
Usually not difficult to identify an unexposed population
Major potential biases when selecting a control group
except if retrospective cohorts
Long, sometimes very long except if retrospective cohorts
Difficult, loss to follow up
No follow up
Many staff, large data sets
Easy to understand
Difficult to understand particularly if case cohort or density case control study
Major if studying risk factors.
Interruption of study if exposure shown to be harmful.
Need for intermediate analysis.
None since outcome already happened.
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