sampling if stratifying is done on a variable that is associated with the variable of interest.
(E) Stratified random sampling has less variability between different samples than simple random
sampling if stratifying is done on a variable that is not associated with the variable of interest.
A researcher is conducting a study to see if a new drug will reduce blood pressure more than the
current drug. One hundred patients recently diagnosed with high blood pressure have volunteered for
the study: 42 of the volunteers are female, and 18 of the volunteers are cigarette smokers. The
researcher does not think there is much difference in blood pressure between males and females, but
she does think there is a great deal of difference in blood pressure between smokers and nonsmokers.
If she uses a randomized block design, she should
(A) block on smoking habits because blood pressure is likely to be associated with smoking habits.
(B) block on smoking habits because the groups are very different in size.
(C) block on gender because there is likely to be little association between blood pressure and
smoking habits.
(D) block on gender because the two gender groups are closer to the same size.
(E) block on both gender and smoking habits because the more variables used for blocking, the
better.
- A high school teacher conducts an action research project as a part of his master’s degree program.
He wants to see if a particular teaching method improves student learning on a particular topic. He
decides to try one method with his morning class and the other with his afternoon class. The two
classes are taught in different rooms. Which of these explains why confounding has entered this
experiment?
(A) If one class does outperform the other, the teacher can’t tell whether it is the teaching method or
the time of day that caused the difference in performance.
(B) If one class does outperform the other, the teacher can’t tell whether it is the teaching method or
the way the groups of students were scheduled that caused the difference in performance.
(C) If one class does outperform the other, the teacher can’t tell whether it is the teaching method or
the different classrooms that caused the difference in performance.
(D) Choices A, B, and C all describe possible sources of confounding.
(E) None of these choices describes a possible source of confounding.