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Thread: Standard deviation

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    Standard deviation




    Hello
    To solve the exercise below, I need the standard deviation =σ I have no clue to get it out of the values below:

    A researcher wants to know if the average time in jail for robbery has increased from what it was several years ago when the average sentence was 7 years. He obtains data on 400 more recent robberies and finds an average time served of 7.5 years. A 95% confidence interval for the average time served is:

    I have tried the mean of 7 and 7.5 with a n of 2 (standard deviation formula) but that is wrong. I think I get it from the proportion, but then I have no p.
    Thank you for your help,
    Roger

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    Re: Standard deviation

    This is not a proportions problem so you really can't do anything without a standard deviation. You'll need more info to solve the problem.
    Last edited by Dason; 01-09-2015 at 01:38 PM.
    I don't have emotions and sometimes that makes me very sad.

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    Re: Standard deviation

    I thought that.... lost almost hours on that...
    Thank you

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    Re: Standard deviation


    Also I reread what I wrote and I forgot the "not". Shouldn't change much though - you still need the standard deviation or other information that allows you to figure out the standard deviation.
    I don't have emotions and sometimes that makes me very sad.

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