Categories like completion percentage, yards a carry and punt return average are concrete. Just take two numbers, divide them and you get the result instantly.
One of the most debated statistics -- the passer rating -- is the toughest to calculate and the toughest to put a premium on.
But is it important?
It isn't important: Mark Brunell had an 86.5 rating when he was benched after nine games (the Washington Redskins were 3-6), including four games of over 100.
It is important: Thirty-six quarterbacks have combined for 101 games with a rating of 100 or better. Their teams are 82-19 in those games.
It isn't important: In two of his team's wins this season, Chicago's Rex Grossman had ratings of 1.3 and 10.2.
It is important: Among the 12 highest-rated quarterbacks in the league that will start games this week, nine would be in the playoffs if the postseason started today.
"It's an evaluation of where the quarterback is in regard to his production," Washington Redskins associate head coach-offense Al Saunders said. "I think it's a great barometer."
Green Bay quarterback Brett Favre, who has four 100-plus rating games this season (all wins), called the statistic "overrated."
"I couldn't even tell you how to figure it out," Favre told the Dallas Morning News last week.
The formula uses attempts, completions, yards, touchdowns and interceptions to come up with a final answer. Many Web sites -- www.brucey.net/nflab/statistics/qb_rating.html, for instance -- can calculate ratings.
The most important number is touchdowns. Two weeks ago, if Jason Campbell threw 59 yards to Chris Cooley -- to the 1-yard line instead of a 60-yard touchdown -- his passer rating would have been 59.5 instead of 74.2.
Through four starts, Campbell has a 68.8 rating.
"The thing that makes it an accurate gauge is the fact it takes into account touchdowns, interceptions and big plays," Redskins quarterbacks coach Bill Lazor said. "But I'm sure there are times where it isn't always accurate."
Saunders said a 90 rating is his benchmark. When Brunell was over 90, the Redskins were 3-1. Campbell is 0-1 when over a 90 rating -- he had a 92.3 rating at Tampa Bay. Marc Bulger of St. Louis has the most defeats (three) when he has a rating of 100-plus.
"In my eyes, if your quarterback gets to 90, he's playing at a high enough level to give you an opportunity to win," Saunders said.
Six current starters have 90-plus ratings for the season; five have winning records.
Even though Drew Brees (the only quarterback over 100) already has passed for more than 4,000 yards and leads the league with a 101.2 rating, Peyton Manning's record of 121.1 in 2004 is safe for another season.
Favre, who has a 78.0 rating this season, said his main problem with the formula is that it doesn't account for the little things.
"Throwing touchdown passes is important, completing passes is important, completing them to your own team is important," he said. "But I've had games where I was pretty darn good and we lost. I had games where I was just OK and we won. Some of that has to do with me, and some of it doesn't.
"Some of the things they factor in are great. But some of the things they leave out -- leadership, how he manages a game, does he block on a reverse -- are stuff that probably aren't as obvious as completion percentage."