The effects of nonresponse in a prospective study of cancer

Out of 11,136 Japanese men identified on the island of Oahu, Hawaii, in 1965 by the Honolulu Heart Program, 8006 responded to a mailed questionnaire and were examined, 1871 only responded to the mailed questionnaire, and 1259 did not respond at all. After 10 years of follow-up, the examined men had a significantly lower risk of death from all causes, death from cancer, and incidence of stomach cancer than the unexamined men. Minimal differences were also noted between the two groups in the time interval between the beginning of follow-up and the diagnosis of cancer of the lung and large bowel, and these favored the examined men. The examined men had a higher risk of prostate cancer incidence, although not significantly so. When the 8006 examined and 1871 unexamined men who responded to the mailed questionnaire were evaluated with respect to the association of cigarette smoking with lung cancer incidence, the odds ratio estimate for smokers was 19 for the examined men and 7 for the unexamined men. However, since these odds ratios are not significantly different, there would be little bias in odds ratio estimates of cigarette smoking for lung cancer if the observation was limited to examined men. With regard to the association of low education with stomach cancer, the odds ratio estimates were nearly identical as 1.2 for the examined group and 1.1 for the unexamined group.