Midgets

So that last entry about the obsolescence of phone books reminded me of something that's been bothering me for a while: When did "midget" get replaced by "little person?" I'm all for eliminating offensive terms . . . but only when they're actually offensive. I feel like in this case, the change was actually made for the worse. At least "midget" denotes some sort of condition; it seems diagnosable. But "little person" seems way more demeaning, doesn't it? It's like saying, "yeah, you're like a person, only littler." Isn't that worse? Can someone please explain to me why that was determined to be the preferred nomenclature?