this is a somewhat basic question:

I have a causal model with 2 endogenous (X, Y) and 3 exogenous (A, B, C) LV's. A and B are antecedents of X (R-Square 50%). C together with X are antecedents of Y (R-Square 60 %).

In this case, there are only

**direct effects**from C and X on Y (no arrow between C and X).

When modeling a

**partial mediation**(i.e. indirect effect from C to Y through X) I get the following results: R-Square of X increases (positive f-square) but R-Square of Y decreases (negative f-square).

How can this result be interpreted adequately, since I can not estimate a "total effect"? Is this a kind of "method factor", because there is an "additional path"?

Thanks for any comments,

Samy