What do we do to study the cause of disease when we cannot or should not expose people to disease risk (i.e., manipulate the independent variable). For example, while we want to understand Ebola transmission and outcomes, legally and ethically we cannot & should not expose people to Ebola risk factors. We cannot do Ebola experiments on people.
Thus, we have to observe what happens when nature takes its course. One common research design in which we let disease/nature take its course is a case-control study. What is a case-control study?
Here’s a quick explanation. The researcher looks for people who have (or had) the disease and then looks back in time at their history of exposure to risk factors for the disease. Those who have been exposed and who did not (or not yet) get the disease are the control subjects. If risk factors for the disease are not well-known then it may be difficult to find control subjects because we would have a hard time telling who was exposed.
Case-control and other studies in which we look back at what happened in the past are called retrospective studies. (In contrast, most nursing studies are prospective studies—in other words they start at the present and move forward. For example, if we were doing research on Ebola symptom management, we would try out symptom management strategies on persons with Ebola and measure into the future how well those strategies work.)
A great flow diagram and clear explanation of case control studies is at http://www.ciphi.ca/hamilton/Content/content/resources/explore/fb_case_v_cohort.html . Check it out!
Critical thinking practice: If you were to design a case-control study related to information in the excerpt below, answer these questions:
- Who would be the case subjects?
- Who would be the control subjects?
- What are the risk factors?
- Why would the study be retrospective?
“Ebola virus, a member of the Filoviridae group, is transmitted by direct contact with blood, secretions, or contaminated objects and is associated with high case-fatality rates (28). Investigations of outbreaks in Africa suggest that Ebola infection may be more severe during pregnancy and that mortality rates are higher. Pregnant women infected with Ebola more often have serious complications, such as hemorrhagic and neurologic sequelae, than do nonpregnant patients (31). Unlike risk for death from Lassa fever, which is highest during the third trimester of pregnancy, risk for death from Ebola is similar during all trimesters (33).” (Jamieson et al, 2006, http://wwwnc.cdc.gov/eid/article/12/11/06-0152_article)