Any guesses - what percentage of authors and actors use pseudonyms or stage names?

Authors: We all know that Ed McBain and Evan Hunter were the same person, and that Mildred Grieveson was the real name of Ann Mather and Caroline Fleming.

Actors: Joan Fontaine was really Joan de Havilland, David Bowie was David Robert Jones, and Declan Patrick MacManus is really Elvis Costello. Let’s not forget that Allen Stuart Konigsberg is Woody Allen.

How prevalent is taking a stage name?

I don’t mean using a nickname (Bob for Robert, Ted for Theodore, Lizzy for Elizabeth) – I mean a totally different name.