# Math Help - Gaussian integral as an average

1. ## Gaussian integral as an average

OK so we have:
$\int f(z) e^{a g(z)} dz^3$
integerated over all space.
Now there is a identity for this integral as an average, or something like that, right? What is it? Or perhaps you have suggestions where I could read up on that kind of thing?
(I'm not looking for the integral in terms of a determinant by the way, or am I? :/ ).
Any help would be much appreciated. Thanks.

2. Maybe if I say expectation value rather than average?