Sometimes, the simplest questions have the most complicated answers. Peyton Manning has thrown 16 touchdowns so far this season, putting him on pace for 64 touchdowns this year. Now, we can be reasonably sure that Manning’s true ability level — even with Wes Welker, Demaryius Thomas, Eric Decker, and Julius Thomas — isn’t four touchdowns per game. But he doesn’t need to keep up that pace to break Tom Brady’s single-season record of 50 touchdown passes: Manning “only” needs to averaged 2.92 touchdowns per game over the final 12 games. But to figure out his odds of averaging nearly three touchdowns per game, we need to figure out his true ability level. So how do we determine that number?

Even for a man who averages four touchdown throws per game over four games, averaging nearly three touchdowns per game going forward is still a tall order. Footballguys.com projected Manning to averaged 2.38 touchdowns per game this year. In 2012, he threw 37 touchdowns, an average of 2.31 touchdowns per game. From 2003 to 2012, excluding games ^[1]That was after removing week 17 of the ’04, ’05, ’07, ’08, and ’09 seasons, and week 16 of the ’05 and ’09 seasons, when Manning left early. Why did I pick the last ten years? I don’t … Continue reading he exited early, Manning averaged 2.17 touchdown passes per game. As a Colt, Manning averaged 1.92 touchdowns per game.

It doesn’t take any advanced math skills to figure out that Manning is likely to average somewhere between 2 and 4 touchdowns per game over the rest of the season. But that doesn’t help us very much: we need to be precise, since the threshold he needs to hit is 2.92 touchdowns per game. I’ll get to the more complicated math in Part II. For now, let’s look at some history.

Prior to 2013, 33 quarterbacks threw at least 11 touchdowns in their first four games. They’re all presented in the table below; let’s walk through Kurt Warner to guide you through the table. In 1999, Warner threw 14 touchdowns in his first 4 games, an average of 3.5 touchdowns per game. He played in 12 games the rest of the year, producing 27 touchdowns, an average of 2.25 touchdowns per game over the rest of the season.

What does this mean for Manning 2013? One thing we could do is run a regression using two variables: touchdown passes per game through 4 games and league average touchdown passes that season. I ran those numbers and the best-fit formula was:

-1.57 + 0.57*TD(4G) + 1.24*LgAvg

The p-value on both variables was not statistically significant, and the R^2 was just 0.05. In other words, I wouldn’t put much stock in this formula. On the other hand, this is a good way to ballpark Manning’s projections. And even if the variables aren’t statistically significant, the results seem reasonable. Essentially, this formula tells us that the league average variable is 2.18 times as important as the TDs-per-game-through-four games variable, which makes sense: four games is a really tiny sample size.

If we assume 1.5 touchdowns per team game will be the league average in 2013 ^[2]A reasonable projection, since the average was between 1.45 and 1.48 in each of the last three seasons, and the average is at 1.61 right now, but the average is generally a bit higher in September, then plugging in Manning’s four touchdown per game average would give him a projection of 2.56 touchdowns per game the rest of the year. That would put his 2013 year-end total at 47, a pretty reasonable projection as of Sunday morning.

Anyway, this is just the Part I; in Part II, I’m going to use a different formula to come up with a more precise projection.