SOLUTION: Amedical researcher wishes to determine the percentage of females who take vitamins he wishes to be 99% confident that the estimate is within 2 percentage points of the true propo

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Question 615011: Amedical researcher wishes to determine the percentage of females who take vitamins he wishes to be 99% confident that the estimate is within 2 percentage points of the true proportion a recent study of 180 females showed that 25% took vitamins. how large should the sample size be? if no estimate of the sample proportion is available how large should the sample be?
I do not know how to find what the sample size should be? so I am completely lost on this problem-I don't know where to start help!
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
A medical researcher wishes to determine the percentage of females who take vitamins he wishes to be 99% confident that the estimate is within 2 percentage points of the true proportion a recent study of 180 females showed that 25% took vitamins. how large should the sample size be? if no estimate of the sample proportion is available how large should the sample be?
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Since E = z*sqrt(pq/n),
n = [z/E]^2*pq
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Your 1st problem:
n = [2.5758/0.02]^2*0.25*0.75 = 3110
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Your 2nd problem:
Use p = 1/2 as the best unbiased extimate.
n = [2.5758/0.02]^2 *0.5*0.5 = 4147 when rounded up
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Cheers,
Stan H.
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