A study is done to determine the relationship between use of oral contraceptives and cervical cancer. Study subjects include 50,000 women who are using oral contraceptives and 50,000 women who have had a tubal ligation. After 2 years of follow-up, the rate of in situ cervical cancer is 18 per 10,000 in the oral contraceptive group and 3 per 10,000 (p < 0.05) in the tubal ligation group. Which of the following is the estimated relative risk of cervical cancer among women who have had a tubal ligation compared with women who use oral contraceptives?
a) 3/50,000=0.00006
b) 3/18=0.17
c) 18/3=6
d) 18-3/10=17.7
e) 18-3=15
f) 18/3=21
g) Indeterminable from the data given