Those lovely and not at all sinister corporate types at Google have devised a new toy called Books Ngram viewer. It lets you graph the number of reference to a particular word or phrase over time in many published works. When I typed in ghost, vampire, zombie and werewolf I found that ghost is way ahead, but vampire put a right old spurt on lately. Teenagers, eh? Poor old zombie and werewolf didn't get a look in. I couldn't include mummy for obvious reasons.