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Confidence intervals

  1. Mar 15, 2006 #1
    What is the value of za/2 for an 80% confidence interval?
    a. .255.
    b. 1.28.
    c. .0398.
    d. .525.

    i know the answer is a, but does anyone know how to calculate that :blushing: ?
  2. jcsd
  3. Mar 16, 2006 #2


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    Science Advisor

    Not in any easy manner- you look it up in a table!
    Here's one on the internet:
    http://people.hofstra.edu/faculty/Stefan_Waner/RealWorld/normaltable.html [Broken]
    Last edited by a moderator: May 2, 2017
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