Is there data anywhere on median income in previous iterations of CDs? I'd be interested in knowing how long ago this became the norm. (I'd imagine if you looked at the 10 wealthiest CDs that were in effect from, say, 1922-1932, they'd all be represented by Republicans, for example.)
About three minutes on Wikipedia and knowing where to look has given me a likely counterexample:
http://en.wikipedia.org/wiki/Sol_BloomThe Upper East Side (surely one of the richest areas back then?) started sending Democrats to Congress all the way back in 1922.
