A new type of screening for lung cancer, computed tomography (CT), has been developed. Medical physicists believe CT scans are more sensitive than regular X-rays in pinpointing small tumors. The H. Lee Moffitt Cancer Center at the University of South Florida is currently conducting a clinical trial of 50,000 smokers nationwide to compare the effectiveness of CT scans with X-rays for detecting lung cancer. (Todays’ Tomorrows, Fall 2002.) Each participating smoker is randomly assigned to one of two screening methods, CT or chest X-ray, and their progress tracked over time. In addition to the type of screening method used, the physicists recorded the age at which the scanning method first detects a tumor for each smoker.

a. Identify the experimental units of the study.

b. Identify the two variables measured for each experimental unit.

c. Identify the type (quantitative or qualitative) of the variables measured.

d. What is the inference that will ultimately be drawn from the clinical trial?