Case 1:
If the 2 samples are of same size:
i.e.,
If Size of Sample 1 = n1 = Size of Sample 2:=n2:
the sample difference is same as the difference of the means,
because of the formula: E(X - Y) = E(X)- E(Y).
Case 2:
If the 2 samples are not of same size:
i.e.,
If Size of Sample 1 = n1 Size of Sample 2:= n2:
For example: there are 51 subjects in the death category and 49 in the survival category :
the sample difference different from the difference of the means, In fact E(X - Y) cannot be calculated because X and Y are of different dimensions.
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