I don't have any research, just a rule of thumb: refactor when it hurts. In my experience, it's easy to go too far in the other direction, trying to craft perfectly generic code on the first pass. That doesn't work very well.

It's important to have a meta-awareness while programming - how firm is your grasp on the code? How confident are you that your changes will do what you expect? At some point, you feel that grasp slipping, and then it's time to refactor.