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t-test weird degrees of freedom

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laurie
laurie 2012-6-6
评论： Fatemeh Shomal Zadeh 2020-12-3
Hi,
I did some t-test (two-tailed) and keeps geting weird degrees of freedom.
I have some pairs of vectors, all of size = [1 144], so n=144 observations for each group
ttest gave me the expected df (142) for some tests, but I also got 139 in another one, and even... 124 in an other one.
What is going on ? Why is the degree of freedom not 142 in all those tests ?
Thank you
  1 个评论
Fatemeh Shomal Zadeh
Fatemeh Shomal Zadeh 2020-12-3
Hi,
Sorry, can you help me and explain how I can get DoF (degrees of freedom) from my test?
Thanks

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Tom Lane
Tom Lane 2012-6-6
I can think of two possibilities. First, if you have any NaN values, they are treated as missing and the df would be reduced accordingly. Second, if you ask for a test based on 'unequal' variances, the df is computed using a Satterthwaite approximation and may be a non-integer.
  2 个评论
laurie
laurie 2012-6-6
thanks ! it was a bit of both actually !
Fatemeh Shomal Zadeh
Fatemeh Shomal Zadeh 2020-12-3
Hi,
Sorry, can you help me and explain how I can get DoF (degrees of freedom) from my test?
Thanks

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