Can someone tell me why Northern Illinois has a slightly higher RPI than the Cats? They are 17-8 with a solid loss AT Missouri, a team that we beat, and their schedule has hardly been laced with cupcakes including Roosevelt! Got their best win by one at home against 20-5 Akron the other night, but their conference has no one even close to the top 25 and no one that's beaten anybody of note all year.
The reason is that RPI is not a sophisticated way of ranking teams.
The RPI has three components: a team's own winning percentage (25%), opponent winning percentage (50%), and opponent's opponent winning percentage (25%), with no rewards for margin of victory or anything else. As a consequence, games against the top teams in small conferences (win or loss) are especially useful, while 40-point victories against 5-25 teams can be very harmful, indeed. For example, going 0-20 against the "top 10" teams losing by 50 points/game, would be better RPI-wise than going 20-0 vs bottom-feeders winning by 50. Interestingly, RPI doesn't count games against non-D1 opponents, so you can actually get away with playing worse teams than the ones we've played without screwing up your RPI!
Neither of the schedules mentioned above are particularly realistic, so the issues with RPI usually cancel themselves out over the course of a season. And, it's a lot easier to calculate an RPI than to make a "smart" computer ranking system, so the RPI will probably remain a part of the discussion for some time to come!