Quiz 6, Module Case-control
6. What is the best way to accrue the controls? [Aschengrau & Seage, pp. 239-243]
- Cross-reference the Superfit Fitness Center 's Membership directory with the local hospital's discharge database taking patients treated there for diseases other than the Susser Syndrome.
- Ask the Membership Services of the Superfit Center to provide you with the names of new members who have enrolled in the last year and are active members in good standing.
- Take a random sample of people from the Membership Directory of the Superfit Fitness Center and determine their eligibility criteria. Those eligible will be asked to participate in the study by phone. If they agree to participate, an interview will be scheduled
Answer (a) —
incorrect:
This method would be unlikely to produce enough controls since the majority of Superfit members would not be admitted to the hospital, because they are otherwise a young and healthy population. In addition, inclusion of controls with other diseases may introduce bias because other diseases may also be related to the exposure of interest and thus controls would not be sampled independently of exposure.
Answer (b) —
incorrect:
Given Susser Syndrome's induction time of 6 months, some of the new members will not have the opportunity to be classified as "exposed," meaning that this sampling technique selects controls dependent on exposure status. In addition, this is not a random sample as new members may not be representative of the entire population of those attending the Fitness Center.
Answer (c) —
correct:
Because of the membership at the club, these controls will be representative of the underlying source population from which the cases emerged. Also, you must make sure that they do not have the disease.
