Bioequivalence and Bioavailability Forum

Dear Yu!

❝ You said the method of equivtest 2.0 is right in the former while it is wrong in the latter. Please clarify it.

You are right, I did not express myself clearly.
EquivTest v2 and /PK are using the correct formula in all situations (n₁=n₂ and n₁#n₂), whereas the formula of v1 is only correct for n₁=n₂. The formula of v1 is wrong for unbalanced studies (n₁#n₂).

BTW, the correct method is the 'weighted mean'; an example:
x1 of n1 numbers [1,2,3] is (1+2+3)/3 = 2,
x2 of n2 numbers [4,5] is (4+5)/2 = 4.5.
The weighted mean xw for two groups is defined with (x1n1+x2n2)/(n1+n2), giving (2×3+4.5×2)/(3+2) = 3.
The 'mean of the means' (x1+x2)/2 irrespective of the size of groups (EquivTest 1) leads to (2+4.5)/2 = 3.25.
The bias (in our case +0.25) can be positive or negative, but always drags the overall-mean towards the mean of the smaller group.