F# code organization: types & modules

Question

How do you decide between writing a function inside a module or as a static member of some type?

For example, in the source code of F#, there are lots of types that

Answer 1

In F# I prefer a static member on a type over a function in a module if ...

1. I have to define the type irrespective of the member
2. The member is functionally related to the type I'm defining