# What is the estimate of the standard deviation of the sampling distribution of sample proportion for whenever?

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A Quality Analyst wants to construct a control chart for determining whether four machines, all producing the same product, are under control with regard to a particular quality attribute. Accordingly, she inspected 1,000 units of output from each machine in random samples, with the following results:

23/1000
15/1000
29/1000
13/1000

What is the estimate of the standard deviation of the sampling distribution of sample proportion for whenever this process is under control?

I used the formula for standard deviation for population samples and it didn't give me the right answer.

I think the answer was 0.0044. I have no idea how they got there.

Edited by wholegrain

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I took the average which is 20 and took the square root of that value (p-chart = poisson distribution?)and then divided it by square root of 1000, which didn't give me the correct answer.

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