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Old 04-11-2012
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Stats Case Control versus Retrospective Cohort

What's the difference between case control and retrospective cohort study?
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Case control is commonly a retrospective study but not same as retrospective cohort study.

The difference between the two is : in case control investigator splits individuals by disease status whereas in retrospective cohort, investigator splits study individuals by their exposure status.


First one can provide odds ratio, which is the odds of disease among exposed individuals divided by the odds of disease among unexposed.
Whereas the later provides relative risk, which is a degree of risk/probability of disease occurrence due to exposure compared to non-exposure.
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Totally agree with slumdog

Case-Control Study, you are studying the disease and see if you can associate risk factors to it. Therefore, you use Odds Ratio. Case-Control Studies are typically done for rare diseases, so you have a rare disease and you go and grab that small number of patients and compare them with a control group and study their history and see if there was a risk factor that might have caused their disease.
Note that Case-Control cannot be prospective because you already have the outcome (disease versus no disease) you are just studying what has lead to this outcome. Therefore, you cannot measure incidence.

Retrospective Cohort, you are studying the risk factor and see if you can associate a disease to it. Therefore you use Relative Risk and Attributable Risk. You can measure incidence in prospective and retrospective cohort studies. Note that cohort study can be retrospective i.e you follow the cohort in past time (history) by checking their hospital records for example. For example you can say the incidence of pulmonary tuberculosis was xx% in Asian immigrants who immigrated to the US in the period (2005-2010).


Classic example is Smoking and Lung Cancer:
If you make a study to find out the percentage of smokers among lung cancer patients versus the percentage of smokers among those who do not have lung cancer then this is case-control.
Conversely, if you follow smokers and non-smokers in time and see who develop lung cancer or not, then this is a cohort study.

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Quote:
Originally Posted by StepTaker View Post
Note that Case-Control cannot be prospective because you already have the outcome (disease versus no disease) you are just studying what has lead to this outcome.

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I think there some correction is needed.

Commonly case control studies are retrospective. Although nested case control studies are prospective in nature and are pursued within prospective cohort.
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I agree

Quote:
Originally Posted by slumdog View Post
I think there some correction is needed.

Commonly case control studies are retrospective. Although nested case control studies are prospective in nature and are pursued within prospective cohort.
Agreed. You caught me in this

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