Does this sentence require a comma before causing?

In other cases, administering a questionnaire may sensitize subjects to the topic causing changes in their responses.

I have been searching in my Scott Foresman Handbook for Writers but have not found an example.

Thanks

Yes, it does.

In other cases, administering a questionnaire may sensitize subjects to the topic causing changes in their responses

You see, you need to separate "causing" from "topic", else it means "...to the topic that causes changes in their responses" and not "... may sensitize subjects thereby causing changes in their responses". Can you see the difference?

GM,
I was hoping that you would respond--your other responses that I have read have been "spot-on." Your explanation makes perfect sense; I am somewhat embarrassed that I didn't think of it before--I think it's the "can't see the forest for the trees" phenomenon.
Thanks!
Ken