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Thread: Determing Z score from level of confidence

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    Determing Z score from level of confidence

    How can I determine the Z score, given a level of confidence of 65%. My math book has the z score for .80, .90, .95, and .99 but none other.

    Like for .90, it gives a zscore of 1.645. I tried to look in the table and see how 1.645 matches up to .90, but I see no correlation. Is there some equation I need to use?

    My problem gives me the following

    level of confidence= .65 sample stan deviation= 2.5 sample size = 36

    It asks me to find the margin of error.
    So I simply need to find the corresponding zscore for the level of confidence .65 and multiply it by the stan dev / square root of the sample size
    Last edited by nappyjim; 05-13-2006 at 07:19 PM.

  2. #2
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    JohnM's Avatar
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    You can use the z table (normal distribution table) in your textbook, or you can also use Excel, which has a bunch of stats functions, including determining a z score from a probability, and vice-versa.

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