I've never seen any hard data on that... but I do know that Philly is one of the only counties in the state that still has not adopted the SURE system (Statewide Uniform Registry of Electors) which is supposed to help purge voters off rolls that shouldn't be there...
I've also asked the director of our local election board how deceased voters are removed and they said that each local election board does it themselves from Dept of Health lists... and if the local board is run by a partisan or corrupt jerk and doesn't do it, you are pretty much out of luck as far as forcing them to do it.
It has been reported here on FR many times over. And yeah, I would also like to see it in black and white.