What:

-Compare two groups of patients – one with disease (case), one without the disease (control). 

-Looks for prior exposure/risk factor. 

-Always retrospective

-Measures the odds ratio – odds that the disease group (case) was exposed to a risk factor. 

-Example: Lung cancer group (case) and healthy group (control). “Patients with lung cancer had a higher odds of smoking than those without lung cancer.”

-Different from cohort study which looks at a group with exposure, group without exposure to see if the exposure increased likelihood of disease (relative risk). “Smokers had a higher risk of developing lung cancer.”

 Advantages:

-Easy and fast to collect data since all retrospective. 

-Able to examine rare diseases or diseases with long course in short amount of time. 

-If low prevalence, odds ratio = relative risk. 

 Disadvantages:

-Selection bias

-Recall bias

-Cannot determine disease incidence