How many Americans believe in ghosts?

Anytime I hear the slightest creak in my house, I look over expecting to see a spirit from the beyond. Usually it's just the cat knocking something over, but I still keep looking.

The idea of souls sticking around after death has been around just about as long as any type of human civilization, and ghost stories can trace their origins to the ancient Romans. Whether it's the thrill of the scare or a belief that we'll have a chance to finish any unfinished business even after our mortal bodies are finished, ghosts are everywhere in American pop culture.

From Casper to Swayze to Ghost Hunters to Charlie Brown, you can take your pick of what you'd like the afterlife to look like. But how many Americans actually believe in ghosts?