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Math Help - measuring standard error

  1. #1
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    measuring standard error

    The story: healthy three year olds have a mean weight of 12.1515 and a standard deviation of 1.3448

    I have a sample of children and I'm comparing it to the population of healthy babies.


    the question im faced with is:

    "How many standard errors (to the nearest hundredth) is the sample mean different from the expected mean for a healthy population (e.g. -4.34)"

    sample 1 mean = 12.045 kg so the difference is |12.045-12.1515| and then that is divided by the standard error.

    standard error is given by

    (standard deviation)/sqrt(n) where n is the sample size.



    So the question is which standard deviation do I use? the sample SD or the population SD?

    my guess is that I should use the sample SD, but since we are comparing our sample to the population maybe measuring the distance in means using the population SD is best?
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    Re: measuring standard error

    Hi kingsolomonsgrave!

    If you have a choice, always compare against the population SD.
    The sample SD is (usually) only a bad approximation of the population SD.
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    Re: measuring standard error

    thanks!
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