Question

You are performing a cohort study to look at risk factors for breast cancer in postmenopausal women. If the probability of developing breast cancer among smokers is .05 for the study duration, then if you sample 100 smokers, how many do you expect to develop the disease? Give the expected value +/- 1 standard deviation.

Answer 1

It appears that a binomial distribution applies. In that case the expected number to develop the disease would be the product of the sample size and the probability:
\[\large Expected\ number=100\times0.05=you\ can\ calculate\]The standard deviation is given by:
\[\large \sigma=\sqrt{100\times0.05\times0.95}=you\ can\ calculate\]