Yeh, shocker, isn't it? I'm sure you did check it out at the time, it wasn't your fault! The book came out in 1973, and it was a best-seller and changed psychiatric views on MPD. At the time, it was accepted as correct, but the research behind the book was locked away with the papers sealed and inaccessible until 1998, that's why it took so long for it to be exposed as a fraud. The NYT article I linked is a fascinating read.