Injury Rates and An Extended Season

At the recent owners meeting, the NFL disseminated a study that concluded an increase in the season schedule from 16 to 18 games would not increase injury rates. The report caught a lot of criticism as a halfhearted attempt to obscure the toll a longer season would take on the players. Judy Battista of the New York Times and Mike Reiss of the Boston Globe both point to flaws in the study.

But I suspect there is a fundamental misunderstanding about what the report says and how it's being interpreted. All I really know about the report is that it says, "the NFL's injury rate doesn't increase at the end of the season." There is no doubt a longer season would result in more total injuries. The bigger question is how many more injuries--does the injury rate itself increase?

Much of the criticism of the study focuses on the use of team injury reports, well known for their deceptive omissions. In an excellent article, Bill Barnwell at Football Outsiders found an additional flaw in the study. It left out players who go on the IR. Before you consider players on the IR, it appears that the injury rate peaks at week 10 before it decreases for the remainder of the season. Barnwell explains why this isn't really the case.

Since team injury reports are notoriously unreliable, the best information is actual games missed. Thankfuly, Barnwell provides that data in his article, and it's very interesting stuff. When you factor in the IR, the number of games missed climbs steadily. He concludes, "the data looks totally different, and in a bad way for the NFL..."

The way I see it, however, is that the NFL report is right, no matter what the intent was of its authors. There is no increase in injury rates toward the end of the season. The injury rate is effectively linear. Of course, as the season wears on, the number of players unable to play due to injury will accumulate, creating an upward climbing injury total. Once you go on the IR, you don't come off. This cuts to the heart of the debate about whether players become increasingly susceptible to injury as the season, along with the number of cuts and collisions, wears on.

Here is a graph of the data included in the Barnwell article.

The blue line is the games missed by roster players (those not on the IR). Except for the uptick on the final week, when playoff bound players nurse their wounds and everyone else has their bags packed for the Caribbean, it's very steady. The green line is the number of games missed by IR or physically unable to perform (PUP) players. Note how its slope steadily increases. The red line is the combination of the injured roster players and IR/PUP players.

Here's what I take away from this data. Players on the IR increase at a (very) slightly exponential rate--specifically it's:

#IR = 0.006w2 + 0.1w + 1.6, where w=week.

That .006 term is extremely small, and when combined with the negative camber of the blue line, results in a very linear total, (especially when week 17 is thrown out, although you don't need to.) [Note: By the way, the slight non-linearity of the increase is evidence, however tiny, for the notion that players become more susceptible to injury as they endure the season.]

Ultimately, the total number of players who miss games due to injury is indistinguishable from a linear line (r-squared of .97). Its increase is exclusively due to players going on the IR, which is a one-way check valve.

So will there be more players missing games at the end of the season if the NFL adds two more games? Of course. But it won't be Iwo Jima out there. No explosion of wounded players with "cascading" injuries. It will be a demanding, grueling, even cruel extra two games for the players, but it would barely be noticeable to the fan and to the game itself. I suspect that's what the NFL report is trying to spell out. Even counting the uptick in the final week, each team would average an extra half a missed player by a potential week 19.

Personally, I'm against lengthening the season for a lot of reasons. The nerdiest is that there is a mathematical elegance to 2 conferences, 4 teams per division, 8 divisions, 16 games, 32 teams, and 256 games per season. Please, no 17th game or 33rd team--I'd have to redo all my algorithms and equations! Actually, I just think 16 is plenty. The fewer the number of games, the more unpredictable the season, and I like that.

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9 Responses to “Injury Rates and An Extended Season”

  1. DustinDawind says:

    Just curious... did anyone look at the injury rates in the playoffs and compare those to the regular season? (I haven't read all the linked articles). Of course there are fewer teams in the playoffs and so there's less data, but it would be interesting to see if the injury rate in the playoffs is any different than the injury rate in the last few weeks of the season. If the rate is the same, that would seem to support the NFL's position.

    Overall, I think I'd actually prefer they keep the season at 16 games. For one thing, I'd hate to see so many old records become meaningless. Plus, it seems like a longer regular season & shorter preseason would mean that fantasy drafts would be earlier and have more position uncertainty. I guess it might also mean that fewer teams would have a bye in a given week, which would mean less shuffling of fantasy rosters, so that might be nice.

  2. Brian Burke says:

    Dustin-Yes, some of the articles linked above talk about the playoffs. Understandably, when there's a lot to play for, banged-up guys will suck it up when otherwise they'd sit out. One of the articles mentioned that the week with the lowest missed-game rate is the conference championships. That's understandable and doesn't suggest guys get healthier toward the end of the year. Plus, like you said, the data is pretty thin in the playoffs.

  3. William T says:

    I would watch regular season professional basketball if they only played 256 games.

  4. Brian Burke says:

    On the other hand...Now that I think about it more, there may be an alternative explanation for the non-linear increase in players going on the IR. As the season progresses, going on the IR becomes less costly. If you put a player on the IR after game 2, he's permanently unavailable for 14 games. If you put him on the IR after game 10, he's unavailable for only 6 games.

    As the cost decreases, we should expect more players to be put on the IR. Players with lesser injuries that sideline them for shorter periods will be put on the IR late in the season to free up the roster spot. Earlier in the year, the team may elect to keep the player on the roster and get the player back later in the season.

  5. Anonymous says:

    A bit out of the loop on this. Would player salaries increase by 12.5% with the addition of two regular season games?

    If this is the case then the compensation to risk ratio would be constant given your above analysis (which I think is correct) - so players should be indifferent. Are they? If not the league could consider paying them a premium for whatever utility loss they derive from these extra two games (i.e. less time at disney world) and I'll bet it's not that much once they start talking money.

    Two more meaningful Sunday's a year, one more home sellout per team, two more opportunities to prove you're worth that contract extension...This seems like a win-win for everyone involved. As for records? People still care, MLB has destroyed most of the value of "records," for me, anyways.

  6. Anonymous says:

    has anyone looked at the cost of injuries to the various stakeholders (ie: impact on winning, short/long-term $ cost to team and/or player, length of career, etc)?

  7. J Johnson says:

    Please, I get bored of watching meaningless football: my team was out after week 5 this year. In good years, nothing but home field advantage in the playoffs has been up for grabs after game 10 or 12. I am also sick of seeing the best players age and virtually disappear after 2-4 years.

  8. Anonymous says:

    has anyone looked at the ammount of concussions this year?wow

  9. Anonymous says:

    well i think that the NFL injuries are very important to find a way to take care of them. Why you ask? well, its cause the seattle seahawks everyone knows it will be obtaining the NFL championship by the year "2016". I personally say this because the Seahawks need a new running back. WHY? because they always lose them due to injury. FIX ITT. thanks love
    - masOn

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