I voted at 0%, since it said "since starting 3E." There were a few PC deaths in the older days due to their fellow PCs.
But when I think about it, most of the intentional PC vs. PC moments never resulted in death, only in severe wounding. The only exception that really stands out was in Ravenloft when the one PC decided that he was going to deliberately court the Dark Powers. Finally fed up with his actions, the other two PCs killed him, ending the campaign.