I don't rate books with my contributions in them on Goodreads, but...

...but it seems like I would be the only one who would do so impartially. My ratings would usually bring the overall rating down, because the works are all usually such small-time collections of short stories that the majority of the people rating them, or even the only people, are associated with the publication. Who mysteriously just happen to think highly of it.

(So yes, that means that the reason I have a high average rating for works on Goodreads is because they're all so insignificant.)

Here's the thing, I believe the others may be trying to do it impartially. But they always end up saying "I'm impartially rating every other story in here except my own. Anyway, I think this collection of stories by newbie writers is totally worth four or five stars." (I would say that too sometimes, but only sometimes. With four stars, not five.)

That rather undermines the argument, which someone presented to me, that authors can also honestly rate works like that as readers. It seems like we're prone to be biased.

Of course, the other, even bigger reason why I don't do it is that it would probably look bad anyway.