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Quizzes

Quiz 8, Module Confounding

8. Suppose investigators wanted to control for education as a potential confounder in the design stage of the analysis. Which of the following would be appropriate to control for education as a potential confounder at the design stage?

  1. Create 2x2 tables of pesticide use and breast cancer separately for those with low education, and then for those with high education.
  2. Only enroll people in the study who have less than a high school education.
  3. Match cases to controls on high vs. low education.
  4. Answer choices A and B
  5. Answer choices B and C.
Answer (a) — incorrect: Stratified analysis is used in the analysis stage of the research process. Stratification means the effect of an exposure is evaluated within strata (levels) of a confounder (e.g., looking at the exposure-disease association among those with low education only and then among those with higher education only). Once you calculate the OR's for each stratum (and if they are similar to one another), you then compare them with the crude OR. If there is a large difference (a commonly used rule of thumb is >10%) between the stratified and crude OR's, you can conclude that the variable may be confounding the exposure-disease association.
Answer (b) — incorrect: This method of confounding control is called restriction. While it is a method to control confounding at the design stage, there is another answer choice that is also a method to control for confounding at the design stage.
Answer (c) — incorrect: This method of confounding control is called matching. While it is a method to control confounding at the design stage, there is another answer choice that is also a method to control for confounding at the design stage.
Answer (d) — incorrect: Stratified analysis is not a method to control confounding at the design stage.
Answer (e) — correct: Restriction and matching are two methods to control for confounding at the design stage. With restriction, entrance into the study is determined by whether the subject falls into a pre-determined category of the potential confounder. With matching, study subjects are selected so that the potential confounder is distributed identically across the comparison groups (Aschengrau & Seage, pp. 294-297).