474. A cohort study is done concerning the relationship between exposure to oral contraception and the risk of breast cancer. 1000 women were followed from 2003 to 2007. Results are listed below:
| Breast Cancer + | Breast Cancer – | ||
| Oral contraceptive + | 300 (a) | 200 (b) | a + b = 500
Probability of breast cancer among exposed: 300/500 = 0.6 |
| Oral Contraceptive – | 100 © | 400 (d) | c + d = 500
Probability of breast cancer among those not exposed = 100/500 = 0.2 |
| a + c = 400 | b + d = 600 |
Which of the following represents the absolute risk reduction of breast cancer in women who do not use oral contraceptives?
- 75%
- 67
- 40%
- 50%
- 30%
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3. or 40%
2 terms you need to know, control even rate (CER) and experimental even rate(EER). here it is 100/500 for CER= 20%. and EER = 300/500 = 60% which you would expect to be higher as those on OCP have a higher incidence of breast cancer, therefore the absolute risk reduction (ARR) is 60%-20% which is 40%, answer is C