Cohort Studies Flashcards
Cohort study
Also called prospective study in contrast with case-control studies which the to be called retrospective studies.
Cohort studies are not always conducted in real time just as case control studies. The key concept to remember is that in cohort studies the exposure status is always determined before the outcome.
Collection of data
Collecting data on exposure now allows the most up to date methods of measurement to be used and bias in exposure classification to be minimised.
However it carries with it the problem of the time lag until effects of the exposure appear. If the disease is of short latency and is relatively common this may be of no importance.
Exposures
These are observational studies and thus the exposure has not been randomly assigned to the groups studied.
This is only of importance if these other different explores are also risk factors for disease.
Measurement
An advantage is that it offers the possibility to look at a range of outcomes rather than just one.
Analysis
In cohort studies tibia usual to estimate the risk or rate of a disease. The risk or rate of a disease in the exposed group is compare to the unexposed.
A common method of presenting the results of cohort studies is by a standard mortality ratio.
Advantages
Exposure is measured before disease onset and is therefore probably unbiased in terms of disease development.
Rare exposures can be examined by appropriate selection of study cohorts.
Multiple outcomes (diseases) can be studied for any one exposures
Disadvantages
Since individuals have to be followed up over time losing contact with them may introduce bias.
The time it takes to carry the study out.
The high monetary cost of doing the study.
Sampling
Aims to mimic the intervention study where individuals are randomly assigned to exposure. In that situation the only difference is the exposure itself.
The selection of appropriate comparison groups is one of the most difficult aspects of cohort studies.
