A randomized trial of fecal occult blood screening for colorectal cancer was conducted in Minnesota.50

a. During a follow-up period of 18 years, the incidence of colorectal cancer that was first diagnosed when metastatic (stage D) in 15,570 persons assigned to annual screening was only 53% that of 15,394 persons assigned to not be screened; for 15,587 persons assigned to be screened every 2 years, the corresponding figure was 68%. Are any other data needed to show that screening was successful?

b. The table below summarizes the mortality experience of the three study groups. In assessing the efficacy of fecal occult blood screening, should attention be focused primarily on total mortality or mortality from colorectal cancer?