A University of South Florida clinical trial of 50,000 smokers was carried out to compare the effectiveness of CT scans with X-rays for detecting lung cancer. (Today’s Tomorrows, Fall 2002.) Each participating smoker was randomly assigned to one of two screening methods, CT or chest X-ray, and the age (in years) at which the scanning method first detects a tumor was to be determined. One goal of the study is to compare the mean ages when cancer is first detected by the two screening methods.

a. Identify the response variable of the study.

b. Identify the experimental units of the study.

c. Identify the factor(s) in the study.

d. Identify the treatments in the study.

e. What type of design, completely randomized or randomized block, was employed?