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    Determine Sample Size




    I'm not sure what direction to go with this problem.

    I'm given 2 random samples:
    1. 120 men, mean age 26.7, standard deviation 5.2yrs
    2. 150 women, mean age 25.1, standard deviation 4.6yrs

    I'm required to 1st construct a 98% confidence interval for the difference in the true mean age between men and women.

    I've done that... interval (0.19, 3.01)
    Bound on the error = 1.41

    Now I have to determine the minimum sample sizes necessary to estimate the difference in the population means to with 1 year with a 98% confidence level assuming equla sample sizes of both men and women and using the estimated standard deviations from above.

    I can determine the sample size for 1 sample. I'm just not sure how to go about setting up for 2 different samples.

    A point in the right direction would be greatly appreciated!!

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    Hi ojvko,

    If you've calculated Sp, the pooled standard deviation for the two samples, you can then get the sample size by solving:

    2.33*Sp*sqrt(1/n+1/n) = margin of error

    2.33 corresponds to 98% confidence.

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    Thanks for the help!!

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