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Math Help - hypothesis and standardized test statistic

  1. #1
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    hypothesis and standardized test statistic

    had to miss my stat class the other day and i'm having trouble on my homework. i got a little but any step by step guidance would be appreciated

    The Department of Economic and Community Development (DECD) reported that in 2009 the
    average number of new jobs created per county was 450. The department also provided the following
    information regarding a sample of 5 counties in 2010.
    County New Jobs Created
    In 2010
    Bradley 410
    Rhea 480
    Marion 407
    Grundy 428
    Sequatchie 400
    a. Compute the sample average and the standard deviation for 2010.
    b. We want to determine whether there has been a significant decrease in the average number
    of jobs created. Provide the null and the alternative hypotheses.
    c. Compute the standardized test statistic. Assume the population is normally distributed.
    d. At 5% (α = .05) significance, test the hypotheses. State your conclusion.


    a) mean = 410 + 480 +407 + 428 + 400 / 5

    Deviation = sqrt[(410-425)^2 + (480-425)^2 + (407-425)^2 + (428-425)^2 + (400-425)^2 / 4]

    = 32.43


    ...and i'm lost now
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  2. #2
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    Your standard deviation and thus your variance is incorrect, what you're looking for is an unbiased estimate of the variance for the population. Take a look through here and I'll help you further, Unbiased and Biased Estimators
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  3. #3
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    why should it be denominator n not (n-1).
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  4. #4
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    Quote Originally Posted by amul28 View Post
    why should it be denominator n not (n-1).
    When working out the variance from a sample, it is usually smaller than the variance of the population, so we divide by (n-1) so that it is a larger number and closer to the actual variance.
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  5. #5
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    I agree hat you said is correct but what njkid110 did also seems correct for me.
    I don't get where i am lost.
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