How much power did the study have for detecting an IRR for breast cancer of 1.5, comparing current OC users vs. never OC users among 40- to 44-year-old women if

(a) The true incidence rate of breast cancer among never users and the amount of person-time for current and never users are the same as in Table 14.31,

(b) The expected number of events for never OC users is the same as the observed number of events in Table 14.31, and

(c) The average follow-up time per subject is the same for both current and never OC users? 

Cancer

The data relating oral-contraceptive (OC) use and the incidence of breast cancer in the age group 40ˆ’44 in the NHS are given in Table 14.31.

Table 14.31: Relationship between breast-cancer incidence and OC use among 40- to 44-year-old women in the NHS

 

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Number of Number of OC-use group person-years 4,761 121,091 cases Current users Past users Never users 13 164 113 98,091