What does a censored observation in 1992 mean in the context of these data? 

Cancer

A study was performed to compare breast cancer incidence between postmenopausal women who used PMH vs. women who did not. A group of 200 women who were current PMH users and 1000 women who were never PMH users in 1990 in the NHS were identified. All women were postmenopausal and free of cancer as of 1990. The 1200 women were ascertained for incident breast cancer by mail questionnaire every 2 years up to the year 2000. However, not all women had complete follow-up. For simplicity, we will assume that women can only fail every 2 years, i.e., in 1992, 1994, . . . , 2000. The results are given in Table 14.36.

Table 14.36 Relationship between PMH use and breast cancer incidence among 1200 women in the NHS

 

^aFailed means developed breast cancer.

^bAssume that at any given year that the failures occur just prior to the censored observations in that year.

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Current PMH users Never PMH users Number of women Number of women Failed In risk set In risk set Year Censored Failed Censored 1000 988 975 200 1990 1992 1994 1996 12 10 22 2 3 2 3 199 194 190 185 4 944 23 193 1998 50 914 133 131 107 716 2000