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Thread: t-test and normality

  1. #1
    Junior Member
    Oct 2010

    t-test and normality

    I keep reading that in order for a t-test to be valid the data need to be normal. I have distributions which are clearly skewed to the right (long right tails) so they are not normal. However I have a sample of of n>100 in both bases so the sampling distributions are essentially normal.

    My question therefore is: does the t-test requirement for normality refer to the original distributions for the raw data, or for the sampling distributions for the sample means?

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  2. #2
    Master Of Puppets
    pickslides's Avatar
    Sep 2008

    Re: t-test and normality

    The t-test itself, tests the sample mean, which will be normally distributed.

    If your data itself is skewed but n is large enough the t-test is considered a robust test.

    I would recommend using a t-test and then using a different test, maybe a non-parametric test like the Kolmogorov-Smirnov test.

    Are the data sets considered different in both tests?
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