Intro to CHIP, Part 1

The very keenest observers of the NHL will have noticed that hockey is occasionally a physically demanding game, which occasionally results in players suffering from less than optimum health over the grind of lengthy seasons and/or labor disputes.

Across a couple of introductory posts, I will take a look at some of the measures of injury occurrences at team level and what data collected between the 2008-09 and 2012-13 seasons can tell us.

In future posts, I intend to flesh out summaries of team-by-team experience across the five-year period and take a closer look at breaking down the data at individual game level.

The basics

Man-games lost (MGL) to injury is the statistic most commonly referred to. MGL figures are recorded and published on a pseudo-official basis by the vast majority of NHL teams, but these figures are not aggregated by the league, nor is there necessarily any consistency in how teams record the figures.

The most obvious drawback of using raw MGL figures is that they do not account for the value of the absent players. A game missed by Sidney Crosby is indistinguishable from a game missed by any Buffalo Sabre (or played by Ville Leino), for example. Using a player’s cap hit to weight MGL is one way to approximate value. Clearly, this is not perfect as a measure of value by any means, but it is simple, stable, and lends itself to snappy, food-based acronyms. TOI and GVT are alternative options as weightings that I have used at times, although each comes with its own deficiencies, which I won’t delve into here.

Cap Hit of Injured Players (CHIP) represents the per-game cap charge of a player missing a game through injury/illness, i.e. annual cap charge divided by 82.

A few points of detail which might explain any inconsistency between my numbers and “official” team MGL figures:

  • Injury absence data I have used comes from the player profile pages on tsn.ca, cap hits from capgeek.com;
  • Figures generally exclude minor league players (at my subjective discretion) who are often on teams’ IR lists at the start of each season, but include anyone who gets injured while on the active roster during the season;
  • Illnesses are included, but healthy scratches, suspensions, and absences due to “personal reasons” are excluded;
  • Games missed by “retired” players still under contract (e.g. Marc Savard, Mattias Ohlund, four or five Philadelphia Flyers each season) are included in my figures, so bear in mind there are arguably a few distortions caused by this.

Team-by-team MGL/CHIP experience 2008-09 to 2012-13

The table below is a ranking of teams by aggregate CHIP over the past five completed (rather than full) regular seasons, with playoff teams highlighted:

Part 1 diagram 1

Figure 1 – Click to view

Clearly, there is some pretty wide variation here, both across the league within any single season and from year to year for individual teams.

I will break down individual team experience in future posts, but for now, I think the most striking feature here is that there appears to be no obvious strong correlation between playoff qualification and the degree and quantity of injuries/illnesses suffered. The injury/success relationship is investigated in a little more detail below.

There is also no great evidence to suggest that the incidence of injuries in the shorter and compressed 2012-13 regular season was greater than in previous years, despite what much of the post-lockout narrative suggested. The aggregate league CHIP figure as a proportion of the pro-rated cap was actually marginally the lowest of the five year sample.

The same figures aggregated by division (before the 2013-14 realignment):

Part 1 diagram 2

Figure 2 – click to view

While I am hesitant to draw too many conclusions from this, it is still interesting that the Pacific appears to have persistently suffered significantly fewer and less costly injuries (the four teams at the bottom of the aggregate CHIP table above were all Pacific teams), which to this very eastern follower of an Eastern Conference team flies in the face of the prevailing complaints of Pacific teams that the tougher travel schedule was significantly detrimental to their health.

Is it random variation over a relatively short period or a sign of better management and/or prevention of injuries by those teams?

Is there a correlation between injuries and a team’s performance?

To help analyse more closely the relationship between success and injuries, the following is a plot of standings points per game against CHIP per game for each team over the five-year period:

Part 1 diagram 3

Figure 3 – click to view

It is worth noting that it would probably be a slightly better basis for comparison to normalise the CHIP figures to account for the rising cap over the period, but doing so has only a marginal effect here.

Nobody would pretend that injuries are the predominant factor in a team’s overall performance. I, for one, have never heard a coach or GM bemoan his team being depleted by even a single injury. Hence, there is a lot of noise here, as you would expect, but this supports the eye test from the table above – the correlation is weak at best and there are several examples of both heavily injury-hit teams doing well and relatively healthy teams failing.

There is possibly slightly more to read from the margins of the points spread. For example, of the 10 highest points/GP teams, seven were below the median CHIP/GP with the other three close to the median, while of the 10 lowest Points/GP teams, all were above the median CHIP/GP.

Thomas Crawshaw is a UK-born/bred/based hockey obsessive, creator of the CHIP injury metric, occasional blogger and since watching the NHL, winner of as many Stanley Cups as Glen Sather. He doesn’t write often, but when he does, it’s always almost good.

Follow Thomas on Twitter at @LW3H.

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