I'm not sure, but it seems that quite a lot of people drop economics. The least common is (I'd say) Philosophy and Economics, and the other two might be quite evenly spread.
And by my previous post I didn't mean any offence, simply that I don't think PPE warrants elevation over all other degrees because it really isn't that hard. I just meant some people act like because you study PPE you're destined to rule the world...