Variance, Schmariance

To see if my off-handed impression was correct, namely that Saskatchewan had a more variable performance in the round robin than did Team Canada, I entered the team percentage score for each draw into a spreadsheet. Unfortunately, when I try to copy the spreadsheet into Blogger, I lose the formatting.

But here are the results:

Variance Team Canada: 34.854

Variance Saskatchewan: 27.273

The range in performances was from 75 to 89 for Saskatchewan and from 75 to 93 for Team Canada.

It looks as if what I saw as team variance was just a lot more scores in the 70s for Saskatchewan.

And maybe there was more variance in the individual performances on Saskatchewan and that's what stuck in my mind. But I'll leave it to someone else to collect the data and do the stats for that possible hypothesis. The stats are available here.

Plus-Minus Scoring in Curling: it doesn't mean the same thing as it does in hockey

I hadn't seen plus-minus scoring of individual curlers until quite recently. If you're like me, it made no sense because I was thinking in terms of plus-minus scoring in hockey, where a player's plus-minus rating refers to the number of goals scored by that player's team while s/he is on the ice minus the number of goals scored by the opponents while that player is on the ice.

Well, of course that makes no sense in curling because the players (with only a few exceptions) are on the ice for an entire game.

So what does plus-minus mean in curling? It simply is a measure of the number of times a player out-rates (in terms of individual percentage scoring) their opposite number at the same position but on the opposing team. For example, in Draw 17, Kelly Scott shot 88% and Amber Holland shot only 57%, so Scott got a +1 and Holland a -1 for that draw. Then to get a player's +/- rating for the entire tournament, just add up all the pluses and minuses.

Good curlers will have a plus-minus score that is substantially positive for a tournament. Those who are struggling will have large-ish negative plus-minus ratings.

Quite frankly, the +/- rating doesn't really tell me all that much. I'd rather see either a list of the % individual ratings for all players at a given permission (as is shown here) or, failing that, just tell me where they rank (as I did here).