Studying Point Differential in the NFL

After breaking down the AFC and NFC for our season previews, I wanted to get a little more in depth with some of my analysis. Point differentials are a great place to start for team analysis and can help to see what teams got “lucky” pulling out close games and what teams were truly dominant. Many other sites mention what their expected wins actually are but I wanted to include the graph and data for exactly how to make that calculation.

To start, I graphed each team’s win total last season against their point differential. Then I used Excel to graph the “best-fit” line, which estimates how many points a win is worth. The equation for this line was y=0.0255x+8, which means that at a starting point where a point differential of 0 is 8 wins, each point added or subtracted to a point differential will be worth .0255 wins. This means that +39.2 points are needed to safely model a team to 9 wins. The equation had an r-squared value of .84, which is a very strong statistical significance. Below is the graph:

PointDifferentialGraph

As you can see, the point differential was a strong indicator as the teams with higher differentials clearly ended up winning more games. Here’s all of the data, which you can sort by a team’s actual wins, expected wins, or differential. I left it sorted from the teams that got the “unluckiest” to the “luckiest” teams in the column that is simply subtracting their actual wins from their expected wins.

TeamPFPADiffWxWDiff
Detroit Lions372437-6546.342.343
New England Patriots5573312261213.761.763
Cleveland Browns302368-6656.321.317
Seattle Seahawks4122451671112.261.259
Jacksonville Jaguars255444-18923.181.181
New Orleans Saints461454778.181.179
New York Giants42934485910.171.168
San Diego Chargers350350078.001.000
Tampa Bay Buccaneers389394-577.870.873
Carolina Panthers357363-677.850.847
Pittsburgh Steelers3363142288.560.561
Kansas City Chiefs211425-21422.540.543
Chicago Bears375277981010.500.499
Arizona Cardinals250357-10755.270.272
Miami Dolphins288317-2977.260.261
Oakland Raiders290443-15344.100.098
Denver Broncos4812891921312.90-0.104
Philadelphia Eagles280444-16443.82-0.182
Cincinnati Bengals39132071109.81-0.190
Buffalo Bills344435-9165.68-0.321
San Francisco 49ers39727312411.511.16-0.338
New York Jets281375-9465.60-0.397
Green Bay Packers433336971110.47-0.527
Dallas Cowboys376400-2487.39-0.612
Baltimore Ravens39834454109.38-0.623
St. Louis Rams299348-497.56.75-0.749
Washington Redskins43638848109.22-0.776
Minnesota Vikings37934831108.79-1.210
Tennessee Titans330471-14164.40-1.596
Houston Texans416331851210.17-1.833
Atlanta Falcons4192991201311.06-1.940
Indianapolis Colts357387-30117.24-3.765

The top 5 underperforming teams were:

  1. Detroit Lions (2.34 less wins than expected)
  2. New England Patriots (1.76 less wins than expected)
  3. Cleveland Browns (1.32 less wins than expected)
  4. Seattle Seahawks (1.26 less wins than expected)
  5. Jacksonville Jaguars (1.18 less wins than expected)

The top 5 over performing teams were:

  1. Indianapolis Colts (3.77 more wins than expected)
  2. Atlanta Falcons (1.94 more wins than expected)
  3. Houston Texans (1.83 more wins than expected)
  4. Tennessee Titans (1.60 more wins than expected)
  5. Minnesota Vikings (1.21 more wins than expected)

Just a little data to make you think about last season and keep some of what teams are doing early in 2013 in perspective. Pay attention to point differentials every week and not just wins and losses, and your analysis of teams will definitely improve.

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One Response to Studying Point Differential in the NFL

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