Institute:Office of National Coordinator (ONC) Workforce Training Curriculum
Component:The Culture of Health Care
Unit:Evidence-Based Practice
Lecture:Phrasing the clinical question
Harm and prognosis
Slide content:Evidence and Its Limits Continued Case-control study Most common form of observational study Retrospectively identify cases of diseases and match to otherwise similar controls, looking to see if different rate or amount of exposure Useful when condition is very rare or has long development time Classic case was demonstration that DES causes vaginal cancer (reviewed in Swan, 2000) 8
Slide notes:8 A case-control study is the most common form of observational study, and its the most common type of study done to assess harm. There are times when we suspect that something is harmful and we want to find out as quickly as possible. We cant do a prospective study because it might take years to get results, so we look retrospectively. We identify cases of the disease that we think are caused by the harmful agent, and then we match them to controls, thus the name, case-control study . Then we look at the two groups, those who have the disease and those who are the controls, and we see if theres a different rate or amount of exposure. This type of study, for example, enabled us to see that there was not a higher rate of use of breast implants in patients with lupus and rheumatoid arthritis. Similar to cohort studies, case-control studies can be useful when the condition is rare. It can also be useful when the condition has a long development time. In fact, thats how it was determined that the drug DES [D-E-S], which was taken off the market in the 1950s, causes vaginal cancer in women.