Injury reports can be misleading

Nov 5, 2002 2:48 AM

   Assessing the injury picture for an upcoming NFL game is an important part of handicapping. The question is, can we find a way to use the injury information released by the NFL to devise a more methodical, objective method to aid us in predicting how teams will fare?

   The first thing is to look at what data we have on hand. The NFL official injury report for each team tells us which players are hurting, to what degree they are unlikely to be able to play in the next game, and their position.

   The classifications used for the significance of an injury is as follows:

   OUT — the player will not play in the upcoming game

   DOUBTFUL — the player has only a 25 percent chance of playing

   QUESTIONABLE — the player has a 50 percent chance of playing

   PROBABLE — the player has a 75 percent chance of playing.

   Each team releases their evaluations of the health of their players, which is then disseminated to the world. Of course, teams are unlikely to be entirely consistent in how they rate an injury, and some good laughs can often be had from a given week’s list (e.g. when Brett Favre is listed).

   Our belief is all injuries count the same regardless of the player’s position or starting status. It’s not always a given that the starting QB is worth more than his backup. Teams are often better prepared to replace a QB than say a special teams leader.

   The second benefit to treating everything the same (other than ease of use) is going against conventional wisdom. Everyone notices a star RB being out, but few notice a minor player who may actually have a major role.

   With this assumption we can then translate the official injury report for a team into a “player units lost” number along the lines of their own playing status.

   OUT — 1 point

   DOUBTFUL — ¾ point

   QUESTIONABLE — ½ point

   PROBABLE — worth ¼ point

   A team with one player out, one player doubtful and one player probable would score 2.0 player units lost. The simple way to use these ratings would be to play a team in a matchup with a significantly lower “player units lost” number than its opponent.

   Looking at the 2001 regular season, playing the lower “injury level” team in every case would yield a 112-111 record. In other words, no predictive value.

   However, when the difference between two teams was 3 or more player units, the less injured team was a strong bet, covering the line 64 percent of the time (27-15).

   The problem with simply using this week’s injury level is twofold. First, it doesn’t account for the fact that some teams are much quicker to list a player as injured than others, and at a much more severe level (one team’s doubtful is another team’s questionable).

   Second, and more importantly, what really would seem to matter is how a team’s injury level this week compares to the week or weeks before.

   A second rating to calculate could be the “change in player injury units” for this game from the last time the team played. A team with a 5.5 rating two weeks ago and a 3.5 rating this week has improved by 2.0 player units. Conversely a team with a 2.5 rating its last game and a 5.0 coming into this has seen an additional 2.5 player units hit their injury list.

   Testing out this second rating since Week 3, the team with the best change was 106-98 ATS, but a strong 17-5 when the change difference between the team and its opponents was 3.0 player units or more.

   Our final tweak to the “injury capping method” is to use both the “player unit” number for this week and the “player unit” number change from this week to last.

   These are some impressive, albeit preliminary, results. It’s a subject worth exploring in more detail.

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