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Math Help - 95% confident level

  1. #1
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    Question 95% confident level

    The Gibbs Baby Food Company wants to compare the weight gain of infants using their brand versus their competitor’s. A sample of 40 babies using the Gibbs products revealed a mean weight gain of 7.6 poungs in the first three months after birth. The standard deviation of the sample was 2.3 pounds. A sample of 55 babies using the competitor’s brand revealed a mean increase in weight of 8.1 pounds in the first three months after birth, with a standard deviation of 2.9 pounds. Can Gibbs be 95% certain that babies using their products gained less weight?
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  2. #2
    MHF Contributor matheagle's Avatar
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    I would do a one sided t-test.
    You can obtain a one-sided CI as well, not a 2 sided, since you want to show one mean exceeds the other.
    NOW, the next question, are you assuming equal variances, if so you need to pool the sample variances.
    YOU can test to see if you have equal variances, via an F test.
    The two t tests I am recommending are in...
    http://en.wikipedia.org/wiki/T-test
    under
    Unequal sample sizes, equal variance
    and
    Unequal sample sizes, unequal variance
    IGNORE the sample size comment.
    Last edited by matheagle; May 3rd 2009 at 05:49 PM.
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