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. 5±60 10±6 5±2 10±5 5±6

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.   5±60  10±6  5±2  10±5  5±6

anonymous · Answer

The population seems to be binomially distributed with success probability $p=0.05$, and the sample size you're using is $n=100$.

For a binomial distribution, the expected value (mean) is equal to $np$, and the standard deviation is $\sqrt{np(1-p)}$.