Question

​Researchers Wilt et al. (New England Journal of Medicine, 2012) investigated whether surgery, compared to just observation, was (more) effective in improving men’s survival chances after being diagnosed with prostate cancer. The researchers identified 731 men with localized prostate cancer who volunteered to participate. They randomly assigned 364 men to surgery and the remaining 367 to observation. All participants were followed for about 10 years. In those 10 years, 21 surgery recipients died of prostate cancer related reasons compared to 31 observation recipients.

1. Identify the observational units.
A. Men.
B. Men with prostate cancer.
C. Men with prostate cance.
D. Men with prostate cancer who received observation r who underwent surgery.
2. What type of study is this?
A. Experiment.
B. Observational study.
3. What is the primary purpose of random assignment in this type of study?
A. To ensure that subjects are representative of the popu lation of interest.
B. To ensure that the groups are of equal sizes.
C. To create treatment groups that are alike in all aspects zes except for the treatment administered.
D. To improve accuracy of results.
4. Identify the explanatory variable.
A. Whether or not man dies of prostate cancer related reasons.
B. Whether or not man undergoes surgery.
C. Percentage of men who die of prostate cancer related reasons.
D. The number o f men who undergo surgery and the number of men who are just observed.
5. Identify the response variable.

Answer 1

(1) B

(2) A

(3) C

(4) B

Explanation:

(1)

The observational units in this study are the men with prostate cancer.

(2)

As the study involves a treatment and a control group, it is an experimental study.

(3)

The primary purpose of random assignment in this type of study is to create treatment groups that are alike in all aspects except for the treatment administered.

(4)

The explanatory variable or the independent variable, is the variable that is altered to observe the changes in the dependent variable.

The explanatory variable in this case is whether or not man undergoes surgery.

(5)

The response variable or the dependent variable is the variable that is being observed for any changes for the given treatments.

The response variable in this case is whether or not man dies of prostate cancer related reasons.