12/09/2015
What is a case control study
A case-control study is a type of medical research investigation often used to help determine the cause of a disease, particularly when investigating a disease outbreak or a rare condition.
If public health scientists want a relatively quick and easy way to find clues about the cause of, for example, a new disease outbreak, they can compare two groups of people:
Those who already have the disease - 'cases'
Similar people who have not been affected - 'controls.'
A case-control study is retrospective - the researchers look back at data collected in the past, enabling them to test whether a particular outcome can be linked back to a suspected risk factor.
To test for specific causes, the scientists need to formulate a hypothesis about what they think could be behind the outbreak or disease.
They then compare how often the group of cases had been exposed to the suspected cause (risk factor), versus how often the controls had been exposed. If the risk factor has a greater prevalence among the cases, then this is some evidence to suggest that it is a cause of the disease.
Risk factors could be uncovered by researchers studying the medical and lifestyle histories of the people in each group. A pattern may emerge that links the condition under investigation to certain factors.
Case-control research is a central tool used by epidemiologists, who look into the factors that affect the health and illness of populations.
Just one risk factor could be investigated for a particular disease outcome. A good example of this is to analyze how many people with lung cancer, versus how many without, have a history of smoking.
When is a case-control study useful in medical research?
Relatively quick and easycase-control study
To test for specific causes, the scientists need to formulate a hypothesis about what they think could be behind the outbreak or disease. They then compare how often the group of cases had been exposed to the suspected cause (risk factor), versus how often the controls had been exposed.
Because a case-control study is retrospective, it is relatively quick to do, involving the analysis of health events that have already happened, and of risk factors that are in the past.
So there is no need for the scientists to wait and see what happens in a trial that unfolds over a future time course (known as a prospective study).
The fact that the data is already available for collation and analysis means that a case-control study is useful when quick results are desired, perhaps when clues are sought for what is causing a sudden disease outbreak.
This time-saving advantage to case-control studies also means they are more practical than other scientific trial designs if the exposure to a suspected cause is a very long time before the outcome of a disease.
For example, if you wanted to test the hypothesis that a disease seen in adulthood is linked to factors occurring in young childhood, a prospective study would take decades to do. A case-control study is a more feasible option in such a scenario.
Does not need large numbers of people
Numerous risk factors can be evaluated in case-control studies since they do not require large numbers of people to give statistically meaningful results. More resource can be put into the analysis of fewer people.
