Many men over 50 take the PSA blood test. The purpose of the PSA test is to detect prostate cancer early.

Dr. Rene Labrie of Quebec conducted a study to determine whether the PSA test can actually prevent cancer deaths. In 1989, Dr. Labrie randomly divided all male registered voters between 45 and 80 in Quebec City into two groups. Two-thirds of the men were asked to be tested for prostate cancer, and one-third were not asked. Eventually, 8137 men were screened for prostate cancer (PSA plus digital rectal exam) in 1989; 38,056 men were not screened. By 1997, only 5 of the screened men had died of prostate cancer whereas 137 of the men who were not screened had died of prostate cancer (Source: New York Times, May 19, 1998).

a. Discuss why this study seems to indicate that screening for prostate cancer saves lives.

b. Despite the results of this study, many doctors are not convinced that early screening for prostate cancer saves lives. Can you see why they doubt the conclusions of the study?