Put a math guy and a volleyball guy together and strange things happen.
The motivation for this was we don't cover volleyball enough, basically. The symbolism of our label counts is notable: as I write this, football has 673 posts, basketball 490, hockey 369, and then all the way down there at 42 is volleyball—behind the CFL (153) and not even half of the NCAA (91). And last I checked, this isn't called The NCAA Blog. (If it were, we'd be doing a lot more work.)
However, unfamiliarity with players is always an issue when you're trying to cover a nationwide league where games often aren't televised or webcasted. So resident volleyball nut Andrew Bucholtz and I spent a few hours one night hashing out a system for expressing a volleyball player's statistical contributions in terms of points and, ultimately, in terms of wins.
Many things volleyball players do are directly related to points, of course. A kill is by definition one point for their team, as is a block. An error is one point for the other team, so they should lose one point when they commit an error. But we need to consider the context: if the leaguewide hitting percentage is, say, .150, then one kill is worth just 0.85 points above what the average player would be expected to obtain (1 minus .150). This "above average" comparison is the foundation for these rankings, unimaginatively called the Bucholtz rankings in honour of their co-creator.
We established baseline rates for hitting percentage, blocks per set, and services aces per set for each conference and for each position. Adjustments by conference are required due to differences in level and style of play across the country: for example, the hitting percentage in Canada West was .182 last year, but just .159 in the OUA, an extremely significant difference. And we adjusted by position to account for the higher conversion rates for middles, whose attacks are often unsuspected (.219 hitting percentage nationwide) and who often record many more blocks than outsides (0.7 per set vs. 0.3). No positional adjustment was made with respect to service aces.
We should also point out that these rankings don't include digs or assists, so they aren't intended to evaluate setters or liberos, just middles and outside hitters. We've only looked at women's results so far, but the same methodology would easily apply to the men as well.
Take UBC's Liz Cordonier, this year's player of the year, as an example. Given her 527 attempts, we would expect her to have 77 kills minus errors, or a .146 hitting percentage. She actually had a .280 hitting percentage, meaning 148 kills minus errors. Thus, 148 minus 77 gives 71 points that Cordonier added above the average outside hitter in Canada West. We can do this for service aces (4 expected, 24 actual for Cordonier) and blocks (23 expected, 16 actual) and we find that she had a plus/minus of 84.5 points. To convert this to something more meaningful, we divided by 25 (points per set) and then by 3 (sets per match) to get unadjusted matches above average. Finally, we scaled the resulting numbers such that each team's total plus/minus for all of its players roughly added up to that team's record.
In the end, we are able to say Cordonier was worth 2.9 matches (or wins) above average, meaning if you took an average player off a 10-10 team and replaced her with Cordonier, you'd expect that team to go about 13-7. A +2.9 puts Cordonier 10th nationwide, and surprisingly third on her team: Kyla Richey (+3.0) and Jen Hinze (+3.1) both rank ahead. Tops in the country is Montreal's Nadine Alphonse (+4.9), with another Carabin at 17th in Laetitia Tchoualack (+2.3), the 2008 BLG Award winner.
The full women's rankings are here; note that anyone with very little playing time is considered average, because they didn't have enough time to contribute to their plus/minus. This isn't necessarily true, so take the results for anyone with less than 30 or 40 sets played with enough salt as you deem appropriate. Also note that the names are, for the most part, left as they were on the CIS site, so last names like "Vallee-V." and "St.georges" come with the territory.
The seven first-team all-Canadians were mostly at the top of these rankings: only Montreal's Alexandra Lojen (49th) and X's Catherine Thornton (105th) were out of the top 15. In Lojen's case, our decision to ignore assists hurts her, since the Montreal setter had nearly 600 of them. For Thornton, her lack of blocks keeps her down: only 0.12 per set, about one-third the baseline rate we compared her against. One could argue that it wasn't Thornton's job to block, but that's one of the issues we run into with a one-size-fits-all stat like this.
Questions are welcome in the comments below or by e-mail.