Saturday, July 25, 2009

JQAS Article Examines Match-Length Implications of Rally- vs. Server-Only Scoring

In the latest issue of the online Journal of Quantitative Analysis in Sports, Balazs Kovacs presents an article entitled "The Effect of the Scoring System Changes in Volleyball: A Model and an Empirical Test" (the journal requires subscriptions, but free guest privileges are available). The article focuses on the change, implemented about a decade ago in many different levels of volleyball competition, from server-only scoring (with side-outs) to rally scoring.

Back when only the serving team could score, matches could drag on indefinitely if the receiving team kept winning rallies (i.e., siding-out); several plays would go by and the score would remain unchanged. Rally scoring was not necessarily adopted to make matches end more quickly, as the number of points needed to win a set (also known as a game) was increased from 15 to either 25 or 30 (depending on league) coinciding with the introduction of rally scoring (except for fifth games of a match). Rather, the change was intended to narrow the range of how long matches took to play (by eliminating the kinds of long scoreless periods alluded to), which could be helpful for television programming.

Kovacs provided a number of computer simulations of matches, but also presented analyses from actual games (using women's play in the NCAA Division II Northern Sun Intercollegiate Conference), before and after the switch to rally scoring. The key results, comparing server-only to rally scoring, were as follows: "the average match length increased from 92.5 minutes to 99.8 minutes. The variance of the match length has decreased from 27.82 in 2000 to 22.56 in 2001" (p. 8). For readers more familiar with the standard deviation as a measure of spread, the variance is simply the squared SD.

Thus, from this one conference at least, rally scoring appeared to accomplish its aim of providing more regularity to the length of matches. Going beyond the scope of Kovacs's article, a concern I've always had about rally scoring is that it may impair teams' ability to stage comebacks. Hypothetically, take a team that's serving while trailing 14-10 in a game to 15. Under the old system, the trailing team could not lose, as long as it was serving. The leading team would first have to win a side-out (which receiving teams are well positioned to do, as they have first crack at running their offense) and then win a point on serve (which is harder, for the same reason). Under rally scoring, however, the leading team could win the game merely with a side-out.


Anonymous said...

Does this study take into account the time between games and timeouts? I would look at game/set length as well instead of match length. Rally scoring equals more side changes as well as timeouts. I am also wondering if the frequency of time outs increase in rally scoring because it is more likely that the other team pulls away. From what I have heard the change was not only made to make the whole match a less variable time but also the game time less variable as to have natural commercial times for tv.

alan said...

Those are all good points. My impression is that just the total match times were used, the kind of thing that might be listed at the bottom of a box score. Here are the relevant passages from the article, which don't give a lot of detail:

"I analyze the Northern Sun Conference matches because this
was the only conference for which detailed data on the match lengths were available for both 2000 and 2001... There are 488 matches in the dataset, out of which 393 have information on the length of the game in minutes."

JH said...

THis is my first time to your blog. I am interested in the analysis of the volleyball match, things like the total number of jumps per position, distance ran during an entire match na dchange of movement frequency.

Do you know where I can get this information?

Thank you for your help.

alan said...

Welcome JH! I'm not aware of any sources for the kind of data you're interested in. I encourage you to collect the data yourself. You could perhaps video-record matches on TV or find match videos archived online at various colleges' athletic websites. I'd be happy to post your results, crediting you as a guest contributor.