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Math Help - Hypothesis Testing

  1. #1
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    Hypothesis Testing

    Hi guys, I need some help with this one ( mainly "1" and "2" ):

    A research check tails of 40 cats. these are the results:


    average s.d n
    Males 190 15 22

    Famales 180 12 18

    1. check the hypothesis that the tails of the males are longer, with significant level of 10%.

    2. what is the significant of the result ? ( p value )

    3. build a confidence interval of 90% to the mean difference
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  2. #2
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    Quote Originally Posted by weeg View Post
    average s.d n
    males 190 15 22

    famales 180 12 18

    3. Build a confidence interval of 90% to the mean difference
    (\mu_1 - \mu_2) \pm t_{(.9,40-2)} \times \left( \sqrt{\frac{\sigma^2_1}{n_1}+\frac{\sigma^2_2}{n_2  }}\right)

    (190 - 180) \pm t_{(.9,40-2)} \times \left( \sqrt{\frac{15^2}{22}+\frac{12^2}{18}}\right)
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  3. #3
    MHF Contributor matheagle's Avatar
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    You should be pooling the two sample variances if you're using 40-2 degrees of freedom.
    That means you are assuming equal varainces.
    Otherwise if you use the above standard deviation you need Satherwaithe's approximation for the degrees of freedom.
    I would do a one sided test where Ha is the claim that the male's tail is longer on average.
    Last edited by matheagle; July 7th 2009 at 09:08 PM.
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  4. #4
    MHF Contributor matheagle's Avatar
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    My changes...

    \bar x_1 - \bar x_2 \pm t_{38,.05} s_p \sqrt{{1\over n_1}+{1\over n_2}}
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