Originally Posted by aj.
They probably feel it's important to consider more than just yards per attempt in the equation. In your example, a 40% passer looks equal to a 60% passer if you only consider yards per attempt. The question is then, would you rather have a QB who connects for longer plays albeit less frequently, over a QB who connects at a much higher rate but for shorter plays. Who knows what they were thinking when they developed the algorithm.
Like I said, that is my opinion. YPA innately has completion percentage factored into it (YPA = Yards per completion X Completion percent). It just seems to count it twice using YPA and completion percentage in the formula. Personally, I don't see a huge difference in a guy that completes 8 of 20 passes for 100 yards and another that completes 12 of 20 for 100 yards. Indeed it is a personal preference whether someone likes the former or the latter passer.
I think YPA and INT percent have it covered.