Sean McIndoe wrote another piece this week about NHL overtime and the Bettman point (the 3rd point awarded for a game that is tied at the end of regulation—depending on your preferred interpretation, it’s either the point for the loser or the second point for the winner), and it raises some interesting questions. I agree with one part of his conclusion (the loser point is silly), but not with his proposed solution—I think a 10 or 15 minute overtime followed by a tie is ideal, and would rather get rid of the shootout altogether. (There may be a post in the future about different systems and their advantages/disadvantages.)

At one point, McIndoe is discussing how the Bettman point affects game dynamics, namely that it makes teams more likely to play for a tie:

So that’s exactly what teams have learned to do. From 1983-84 until the 1998-99 season, 18.4 percent of games went to overtime. Since the loser point was introduced, that number has up to 23.5 percent. 11 That’s far too big a jump to be a coincidence. More likely, it’s the result of an intentional, leaguewide strategy: Whenever possible, make sure the game gets to overtime.

In fact, if history holds, this is the time of year when we’ll start to see even more three-point games. After all, the more important standings become, the more likely teams will be to try to maximize the number of points available. And sure enough, this has been the third straight season in which three-point games have increased every month. In each of the last three full seasons, three-point games have mysteriously peaked in March.

So, McIndoe is arguing that teams are effectively playing for overtime later in the season because teams feel a more acute need for points. If you’re curious, based on my analysis this trend he cites is statistically significant, looking at a simple correlation of fraction of games ending in ties with the relative month of the season. If one assumes the effect is linear, each month the season goes on, a game becomes 0.5 percentage points more likely to go to overtime. (As an aside, I suspect a lot of the year-over-year trend is explained by a decrease in scoring over time, but that’s also a topic for another post.)

I’m somewhat unconvinced of this, given that later in the year there are teams who are tanking for draft position (would rather just take the loss) and teams in playoff contention want to deprive rivals of the extra point. (Moreover, teams may also become more sensitive to playoff tiebreakers, the first one of which is regulation and overtime wins.) If I had to guess, I would imagine that the increase in ties is due to sloppy play due to injuries and fatigue, but that’s something I’d like to investigate and hopefully will in the future.

Still, McIndoe’s idea is interesting, as it (along with his discussion of standings inflation, in which injecting more points into the standings makes everyone likelier to keep their jobs) suggests to me that there could be some element of collusion in hockey play, in that under some circumstances both teams will strategically maximize the likelihood of a game going to overtime. He believes that both teams will want the points in a playoff race. If this quasi-collusive mechanism is actually in place, where else might we see it?

My idea to test this is to look at interconference matchups. Why? This will hopefully be clear from looking at the considerations when a team wins in regulation instead of OT or a shootout:

1. The other team gets one point instead of zero. Because the two teams are in different conferences, this has no effect on whether either team makes the playoffs, or their seeding in their own conference. The only way it matters is if a team suspects it would want home ice advantage in a matchup against the team it is playing…in the Stanley Cup Finals, which is so unlikely that a) it won’t play into a team’s plans and b) even if it did, would affect very few games. So, from this perspective there’s no incentive to win a 2 point game rather than a 3 point game.
2. Regulation and overtime wins are a tiebreaker. However, points are much more important than the tiebreaker, so a decision that increases the probability of getting points will presumably dominate considerations about needing the regulation win. Between 1 and 2, we suspect that one team benefits when an interconference game goes to overtime, and the other is not hurt by the result.
3. The two teams could be competing for draft position. If both teams are playing to lose, we would suspect this would be similar to a scenario in which both teams are playing to win, though that’s a supposition I can test some other time.

So, it seems to me that, if there is this incentive issue, we might see it in interconference games. So our hypothesis is that interconference games result in more three point games than intraconference games.

Using data from Hockey Reference, I looked at the results of every regular season game since 1999, when overtime losses began getting teams a point, counting the number of games that went to overtime. (During the time they were possible, I included ties in this category.) I also looked at the stats restricted to games since 2005, when ties were abolished, and I didn’t see any meaningful differences in the results.

As it turns out, 24.0% of interconference games have gone to OT since losers started getting a point, compared with…23.3% of intraconference games. That difference isn’t statistically significant (p = 0.44); I haven’t done power calculations, but since our sample of interconference games has N > 3000, I’m not too worried about power. Moreover, given the point estimate (raw difference) of 0.7%, we are looking at such a small effect even if it were significant that I wouldn’t put much stock in it. (The corresponding figures for the shootout era are 24.6% and 23.1%, with a p-value of 0.22, so still not significant.)

My idea was that we would see more overtime games, not more shootout games, as it’s unclear how the incentives align for teams to prefer the shootout, but I looked at the numbers anyway. Since 2005, 14.2% of interconference games have gone to the skills competition, compared to 13.0% of intraconference games. Not to repeat myself too much, but that’s still not significant (p = 0.23). Finally, even if we look at shootouts as a fraction of games that do go to overtime, we see no substantive difference—57.6% for interconference games, 56.3% for intraconference games, p = 0.69.

So, what do we conclude from all of these null results? Well, not much, at least directly—such is the problem with null results, especially when we are testing an inference from another hypothesis. It suggests that NHL teams aren’t repeatedly and blatantly colluding to maximize points, and it also suggests that if you watch an interconference game you’ll get to see the players trying just as hard, so that’s good, if neither novel nor what we set out to examine. More to the point, my read is that this does throw some doubt on McIndoe’s claims about a deliberate increase in ties over the course of the season, as it shows that in another circumstance where teams have an incentive to play for a tie, there’s no evidence that they are doing so. However, I’d like to do several different analyses that ideally address this question more directly before stating that firmly.

Or, to borrow the words of a statistician I’ve worked with: “We don’t actually know anything, but we’ve tried to quantify all the stuff we don’t know.”