Contents
How would you carry out a case-control study?
Five steps in conducting a case-control study
- Define a study population (source of cases and controls)
- Define and select cases.
- Define and select controls.
- Measure exposure.
- Estimate disease risk associated with exposure.
- Confounding factors.
- Matching.
- Bias.
What is the ideal ratio of cases to controls for a case-control study?
Investigators planning case-control studies are usual- ly advised to include no more than four or five controls per case because little statistical power is gained by fur- ther increasing this ratio (1,2).
How many controls does each case have?
An important technique for adding power to a study is to enroll more than one control for every case. For statistical reasons, however, there is little gained by including more than two controls per case.
What is the primary objective of any case-control or cohort study?
Case controlled studies compare groups retrospectively. They seek to identify possible predictors of outcome and are useful for studying rare diseases or outcomes. They are often used to generate hypotheses that can then be studied via prospective cohort or other studies.
How is the odds ratio in a case control study calculated?
The odds ratio is calculated using the number of case -patients who did or did not have exposure to a factor (such as a particular food) and the number of controls who did or did no t have the exposure. The odds ratio tells us how much higher the odds of exposure are among case-patients than among controls.
How are the hypotheses of outbreaks tested?
A hypothesis is tested to determine if the outbreak source has been correctly identified. Investigators use many methods to test their hypotheses. Two main methods are analytic epidemiologic studies and food testing. The most common type of study conducted during foodborne outbreaks are case-control studies.
How are case control studies used in foodborne outbreaks?
Investigators collect information from sick people ( cases) and non-sick people ( controls) to see if sick people were more likely to have eaten a certain food or to report a particular exposure. Case-control studies try to include controls who have had the same opportunities to be exposed to an unsafe food item as a case has.
Which is the best way to test hypotheses?
Investigators use many methods to test their hypotheses. Two main methods are analytic epidemiologic studies and food testing. The most common type of study conducted during foodborne outbreaks are case-control studies.