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Luis A. Afonso
Posts:
4,758
From:
LIsbon (Portugal)
Registered:
2/16/05


About the T test statistics
Posted:
Dec 26, 2013 12:35 PM


Around the T test statistics
From the formula, for the Population difference on means:
T= =(mXmY)/Sqrt[ssd/(nX+nY2)*(1/nX+1/nY)]
Where mX, mY = observed sample means, sizes nX, nY, ssd = ssdX+ ssdY= sum of square deviations.
One can easily obtain a good approximation
T= (mXmY)/Sqrt [(ssd)/(nX * nY)] In fact __(1/nX+1/nY)/[nX+ nY 2] = __[(nX+ nY)/(nX+nY2)]* 1/(nX * nY) = __[1/(1 2/(nX+nY)]* 1/(nX * nY) It can be seen that, unless the total sample is small, the square bracket is very close to 1.
Luis A. Afonso



