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Unformatted text preview: Case-Control Studies Case Control Studies Part 1 Dr. H. Stockwell Case-Control Study: Definition A group of individuals with a disease (cases) are compared with a group of individuals without the disease (controls) Also called a retrospective study because it starts with people with disease and looks starts with people with disease and looks backward for previous exposures which might be relevant to the development of the disease Case-control studies Case-control study is a method of sampling a population in which cases sampling a population in which cases are identified and a sample of the source population that gave rise to the cases is also identified and enrolled (controls) What is the source population The population from which the cases are derived are derived The source population can be difficult to The source population can be difficult to identify Design of Case-Control Studies cases controls exposed a b unexposed c d Total cases = a+c Total controls= b+d Cases and Controls Cases should be representative of all those with disease in the source population Controls should be representative of all those without disease in source population Case Ascertainment Where can you find cases? Selection of Study Cases Hospitals Physicians practice Physicians practices Disease Registries HMOs Others Selection of Study Cases Incident or Prevalent Cases????? Incident vs. prevalent cases Incident cases-newly diagnosed - takes time for them to occur - study takes a time for them to occur study takes a long time to complete Prevalent cases-existing cases - available now but may include many available now but may include many long survivors - not representative of all cases cases Cases Population-based cases: Random sample (ideally Random sample (ideally) All individuals from a defined geographic/political area Hospital-based/medical care system cases: In-patient (admitted) patients to hospitals/clinics Regional disease registries (e.g., cancer reg.) Records of large ambulatory care practices (e g Records of large ambulatory-care practices (e.g., MD offices, HMOs) Case Ascertainment Advantages/disadvantages of finding...
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- Summer '08