When does your starter lose it?

Pizza Cutter has a nice article on what happens to starting pitchers as they stay in the game. My quick interpretation: every ten pitches adds about .04 runs per game, so a pitcher who has a 4.00 ERA at the beginning of a game has become 4.40 ERA pitcher by his 100th pitch. I’m unclear how his methodology handles the selective sample bias, though he says it does (and I trust him!).