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.

Friday, July 3, 2009

Yahoo Group: VolleyStats

A while back, I joined a Yahoo discussion group called VolleyStats. As a result, I've been receiving e-mails from the group that fall into two categories: junk messages and serious reports of statistical analysis from someone named Leo van Hal. Because van Hal's reports are written in Dutch, I really didn't learn anything more about volleyball from them than I did from the junk e-mails.

That situation recently changed, however. I found a new Google application website (new to me, at least) called Google Translate, which is quite easy to use. You simply type (or copy and paste) text from the originating language into a box, select the "from" and "to" languages, and click! van Hal's reports often contain graphs, so rather than copy and paste his entire paper into Google Translate, I do it a few paragraphs at a time, avoiding the graphs. The translations aren't always perfect, sometimes leaving me with odd English constructions. With a little inference ("reading between the lines"), however, I'm confident that I'm picking up the key points.

One message I received was titled "[volleystats] Digest Number 447 [2 Attachments]," dated May 17, 2009. The two attached analyses were titled "Punten verdeling" (Distribution of points) and "Winst Kansen" (Profit Opportunities). Both reports have to do with testing different probabilities of teams' winning points on their serves, and how this affects the probability of different point totals in the games and teams' probabilities of winning the games. (In the English translations, the Dutch word "opslag" appears in English as "storage," but apparently "service" is another synonym; the passages will read much easier in English if you substitute "service" for "storage.")

If you would like English-translated copies of these two van Hal reports, please e-mail me via my faculty webpage in the upper-right portion of this page.