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Thread: Power of Chi square

  1. #1
    Points: 540, Level: 10
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    Power of Chi square

    Hi Guy
    Just wondering if anyone can check if the following calculation is correct please and the right formula has been used? Have posted elsewhere but very worried that this may be incorrect.

    In the original audit there was 15/55 events =27%
    In the re-audit there was 22/55 events =40%
    X2 = 1.99, deg free=1, p=0.15
    Can a power analysis be done?

    I think the answer is "yes". Using the following website http://homepage.stat.uiowa.edu/~rlenth/Power it states to obtain a power of 80% I should have had n=434, ie in the re-audit study I should have studied 379 cases (434-55 cases). See below. Is this correct?

    Thanks again
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