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HiI am testing that data are normally distributed by using

  1. Feb 10, 2012 #1
    I am testing that data are normally distributed by using chi-square test.
    I get a very high chi coefficient about 173.
    This is very strange because data fits at 3sigma test and median mode are equal so I am almost sure that is normal distribution.
    What I am doing wrong?
    Which test do you advice for a better approach?
  2. jcsd
  3. Feb 10, 2012 #2
    Re: Chi-square

    The Central Chi Square will approach the normal distribution as the number of degrees of freedom gets large. For over 50 df, the distribution is effectively normal.
  4. Feb 13, 2012 #3
    Re: Chi-square

    The problem is that I don't have so much degrees of freedom to get this value.
    The other tests Kolmogorov or AD work just fine.
    Maybe I am miscalculating degrees of freedom or 310 data are an issue?
    Please help
  5. Feb 13, 2012 #4
    Re: Chi-square

    Are you saying you have 310 data points? If they are independent observations that would mean you have 309 df. In this case, you certainly should be able to assume a normal distribution with the central chi square. When you say the other tests of normality work fine, do you mean they are consistent with normality? If so, you should be fine. However, I think you might be aggregating data in some way, and how you do this could be important in interpreting the data..
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