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    Sample Size, Margin of error

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    I) Find the minimum sample size you should use to assure that your estimate of p will be within the required margin of error around the population p.
    1) margin of error:0.01; confidence level:95%; from a prior study p is estimated by the decimal equivalent of 55%.

    2) Margin of error: 0.007; confidence level: 98%; p and q unknown

    II) Find the margin of error : 95% confidence level interval; n =91; x (sample mean)= 85, s= 3.7

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    Find the minimum sample size you should use to assure that your estimate of p will be within the required margin of error around the population p.

    1) margin of error:0.01; confidence level:95%; from a prior study p is estimated by the decimal equivalent of 55%.

    Sample size (proportions):

    confidence interval= 95%
    proportion =p= Known = 0.55
    Error= ±z*sp= 0.01 or 1%
    where sp=standard error of proportion=square root of (pq/n)
    Thus we have to ensure that Z* sp < 1%
    Z corresponding to a confidence level of 95.% and two tails = 1.9600
    (from the tables or using EXCEL function NORMSINV)
    Thus, sp < 1.%/Z
    or sp < ...

    Solution Summary

    Calculates sample size and margin of error given confidence interval.

    $2.19

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