### CFA Practice Question

There are 434 practice questions for this study session.

### CFA Practice Question

In estimating the population proportion for the days in summer that have thunderstorms, p, if the sample proportion, p', is 0.35 and the sample size is n = 92, the standard deviation of the sampling distribution is ______ (to nearest 0.001).

A. 0.650
B. 0.350
C. 0.050

For a proportion the standard deviation of the sampling distribution, the distribution of the p's is shown at top right. Working with this formula, we get 0.050.

User Comment
Pieter Where does this formula come from?
savita binomial distribution. The variance is p(1 - p).
StanleyMo excuse me, variance = P(1-p)/n under this situation.
apiccion Savita, variance of a binomial distribution is np(1-p). You're thinking of a Beroulli random variable.
cleopatraliao sampling distribution dealing with mean so we have to divide by n but not binomial, this is different. Just google the difference
johntan1979 http://www.stat.yale.edu/Courses/1997-98/101/binom.htm

pop mean, var = np, np(1-p)
sample mean, var = p, [p(1-p)]/n

Too easy to assume sample var is divided by only one n to become p(1-p) like the mean.
sgossett86 Without reading above... CFAs this was like the last question which i commented on. We saw that sd=(p(1-p))^.5 ... remember that we're finding the sd of the SAMPLING DISTRIBUTION, so we have to plug that into the standard error formula

sd/N^.5

that'll get you to the answer directly.