Don't be an average fan

How do you measure the consistency of a quarterback's performance?

Many fans simply defer to one of the most popular models in all of sports: average. The Cold, Hard Football Facts have a better system. It's allowed us to rate every starting quarterback in the NFL, from the most dependable, rock-solid performers to the most inconsistent pretenders who pull a jittery John Daly alcohol withdrawal imitation each time they step back into the pocket. (Hey, if that's what sobriety does to you, we say keep drinking.)

Fan favorite average, of course, is a hot little number in the world of sports and you see her everywhere. But she's also the air-headed supermodel of the statistician's world. Oh, sure, average has that seductive come-hither look when broadcast on a 16-inch Technicolor TV (yeah, we got a big, new tube!) or when splashed naked across the pages of a glossy magazine. She's also quite popular because, let's face it, as every guy in school knows, average is easy. But put a microphone in front of her face and average doesn't have a whole lot to say. In fact, like any sexy little plaything, average can mess with your head and leave you broke, angry, lonely, drunk ... and, worse, ignorant of the Cold, Hard Football Facts.

To see what we mean, take a look at an example from football: average passing yards per game.

* Player A averages 240 yards passing per game over the first four games of the year.

* Player B averages 200 yards passing over the same four weeks.

The average fan will tell you that Player A is better than Player B. He may very well be right.

But what if Player A's four individual game totals look like this: 145 yards, 155 yards, 325 yards and 335 yards? Well, in this instance, average doesn't tell you a whole lot. In fact, it's virtually useless because not one of Player A's individual performances comes close to approximating his average performance.

Now take a look at Player B. His individual four game totals look like this: 190 yards, 195 yards, 205 yards and 210 yards.

Well, in these examples, Player B is clearly more consistent. In fact, many coaches would probably sacrifice Player A's lofty average in favor of the more consistent performer in Player B. So, too, would most fans. After all, what good is that 240-yards-per-game passer if he litters the field with rotting hambones every other week? Imagine if you wasted an entire week's worth of can-collecting to buy a ticket to see that dog of performance from Mr. 240 Per Game? You'd be pissed.

Fortunately, average has an ugly nerd of a stepsister named standard deviation and she knows a whole lot more about football than her more popular sibling. We swallowed what little pride we have and took standard deviation out on a date – hey, at least she's not fat – and learned all about the most consistent quarterbacks in football last season.

Standard deviation is pretty well educated and has made her mark in many fields. Investment firms rely heavily upon standard deviation. It helps them measure the volatility (or risk) of a particular stock. Some investors don't have the stomach to handle a volatile, high-risk stock that may earn them big money one month but then tank on them the next. They want more consistent stocks. Standard deviation is a tool that sorts out the sexy but inconsistent stocks from those plodding brutes that are more likely to earn investors a consistently positive return.

Without getting too involved, standard deviation essentially measures the distance a quantity is likely to lie from its average value. (You can find the formula for standard deviation and a good description of it here. We simply used an online calculator.) The smaller the standard deviation, the more consistent the set of variables. In our case, the variables we used were quarterback passer ratings.

Here's what we did. We used our online calculator and entered the game-to-game passer ratings in 2004 of every quarterback in the NFL who started 12 or more games. We limited ourselves to only those quarterbacks who played at least 12 games because we felt this gave us a fair set of variables with which we could accurately measure a quarterback's consistency from game to game over the course of a season and, more importantly, compare them to others. It's just not scientifcally reasonable, in this formula, to compare a quarterback who's played just eight games with a quarterback who's played 18.

We weren't surprised to find New England's Tom Brady near the top of the list. Consistency is a hallmark of his career in the NFL. But we were surprised to find Marc Bulger of St. Louis standing unchallenged as the most consistent quarterback in football in 2004. In fact, it was even close.

In Bulger's worst game, at Buffalo, he posted a passer rating of 65.7. In his best game, home against the N.Y. Jets, he posted a passer rating of 116.4. In 16 games, that represented a pretty narrow range of passer ratings. In other words, you knew what you were going to get when Bulger stepped on the field last year. He was rarely spectacular, but he was almost always pretty darn good. That's a good guy to have running your team.

The bottom of the list was filled by players we knew we'd find there even before running the numbers. The most inconsistent quarterback in the NFL in 2004 was Michael Vick. Four times in 2004, Vick posted a passer rating of better than 120, topping out with a 136.1 at Denver on Halloween. But he also played four games in which his passer rating failed to top the 50.0 mark. Fittingly for the most inconsistent QB in the NFL, Vick played his very worst game (a 13.9 passer rating) against Kansas City the week before having his best game of the year against Denver. Anyone who watched NFL football last year saw that Vick could be brilliant one week and a disaster the next. Standard deviation simply provides scientific proof that this observation is correct.

Here, then, is our listing of NFL quarterbacks – from most consistent to least consistent – as measured by the standard deviation of their game-to-game passer ratings in 2004. Remember, the smaller the standard deviation, the more consistent the player's performances.

Obviously, looking at a quarterback's overall passer rating helps us make a further critique of a player's consistency. We were able to group many of these players into one of four categories:

Like we said, sexy little average gets all the acclaim. But it says and means very little without its ugly stepsister standard deviation sitting there to give you some perspective. And, let's face it, average is probably too popular and too hot for a low-life football-loving loser like you.