1. Define restriction
2. What does it provide?
3. What exactly does restriction do? How does this prevent confounding?
4. When is restriction particularly useful? (2)
5. Advantages? (3)
6. Disadvantages? (5)
1. Restriction - restricting participants' eligibility upon enrollment into study (i.e., by age, gender, race, etc)
2. Complete control of known (restricted) confounders
3. Restriction eliminates any possible association between the exposure and the confounder AND between the confounder and the disease. With restriction, there is no longer variability in the values of the confounding variable.
- 4. When confounder is quantitative in scale but difficult to measure
5. (1) conceptually straightforward (2) handles difficult to quantitate variables (difficulty in measurement) (3) can be used in analysis phase
6. (1) limits #
of eligible subjects (2) inefficient
to screen subjects then not enroll (3) residual confounding
may persist of restriction categories aren't sufficiently narrow (4) limits generalizability
(5) can't evaluate the relationship of interest at different levels of the restricted variable (e.g., can't assess interaction)