# 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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 Click here to see ALL problems on Probability-and-statistics 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(57323)   (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? ------- Since E = z*sqrt(pq/n), n = [z/E]^2*pq --- Your 1st problem: n = [2.5758/0.02]^2*0.25*0.75 = 3110 ---- 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 ==================================================== Cheers, Stan H. =======================