In rugby competitions, it is now standard to award bonus competition points to teams that score a certain number of tries in a game. The last holdout competition was the Six Nations, which introduced bonus points only in 2017, over 30 years after they were first introduced in New Zealand's National Provincial Championship (in 1986). In 2016, Super Rugby modified the bonus point, by moving from teams needing to score four tries, to teams needing to score three more tries than their opposition. In all cases, the purpose of these bonus points is to increase try scoring, by creating incentives for teams to score more tries.
As I noted in yesterday's post on child allowances:
...'people respond to incentives'. When economists say that, they mean that when the costs of doing something increase, we tend to do less of it. And if the costs of doing that thing decrease, we tend to do more of it. The reverse is true of benefits - when the benefits doing something increase, we tend to do more of it, and when the benefits decrease, we tend to do less of it.
In this case, bonus points for tries increase the benefits of scoring tries, so teams should try harder (pun intended). But, do these incentives work? In a 2019 article in The Conversation, Liam Lenten (La Trobe University) says yes, and no:
In research to be published in the Scottish Journal of Political Economy, we report that the introduction of the try bonus was effective in increasing the likelihood that teams would score four tries in a match (which is an above-average number).
The effect was concentrated on home teams, which given the advantages they already enjoy are more often in a position to go for the bonus. It would appear to lend support for the view that the rule (or policy, in economist-speak) had achieved what it was meant to...
But not so fast. We also found a significant reduction in teams scoring five or more tries.
That’s right, a reduction.
We believe it was driven by teams reducing their attacking effort once the bonus had been secured, as a large share of teams that score a fourth try already have a comfortable lead, and it is generally late in the game.
It means that, on balance, the evidence in favour of bonus points achieving their aims is mixed. At best they achieve something, at worst they are counterproductive.
The research itself was finally published last year (sorry, I don't see an ungated version), and is co-authored by Robert Butler (University College Cork) and Patrick Massey (Compecon). It was based on data from the European Rugby Cup (or Heinecken Cup, if you prefer) over the period from the 1996/97 to 2013/14 seasons, with a bonus point for scoring four tries introduced in the 2003/04 season.
Butler et al. found that teams that scored at least three tries were more likely to score a fourth try than would be expected based on game and competition conditions. So, there was a positive incentive for try scoring for teams that had already scored three tries, and those teams were putting in more effort to score.
In contrast, teams that had already scored four tries were less likely to score a fifth try than would be expected. So, there was a negative incentive for try scoring for teams that had already secured a bonus point. Those teams were taking their foot off the gas, because there is less incentive to keep running up the score once they had scored four tries.
It would be interesting to see what the incentive effects are for Super Rugby, now that the bonus point is based on net try scoring - where teams need to score three more than the opposition. That rule change has only been around a few years, so it will take much more data collection before a quantitative analysis can be conducted. In the meantime, keep an eye on how the teams are playing when they are close to a three try lead. Super Rugby Aotearoa starts this coming weekend!
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