Sjusjøen Recap

Finally, the World Cup season is under way. The individual 10/15km freestyle races this past weekend had some predictable performances (the Norwegian women) and some not so predictable performances (Swedish men).

Men

Let’s focus on just three of the men with notable performances on Saturday:

Definitely strong races for each of these guys, but there are some differences. Note that in Johan Olsson’s case, the past three seasons have seen him more or less plateau, and maybe even fall off a bit. He hasn’t laid down an effort quite like that in some time. Given his age and the trend over the past few seasons, I’d guess that we aren’t going to see Olsson pull this rabbit out of his hat each weekend, but you never know.

Calle Halfvarsson, on the other hand, is quite young, only around 22 I believe. For some reason I had it in my head that he was more of a sprinter, but looking back at his results I see now that he’s not quite that lopsided. He has racked up a 1st and 5th place in the WJC sprints, and several top 30 appearances in WC sprints, once as high as 9th. His distance results haven’t looked quite as impressive, but they certainly haven’t been poor. One interesting point to make is that after some strong WJC results, Halfvarsson had some strong results in WC races last season, including the sprints I mentioned. But he didn’t fare well at U23’s last year, finishing 23rd, 25th and 27th. This is a good reminder that you can’t put too much emphasis on a single set of championship level races in evaluating skiers.

All that said, this Saturday’s race was clearly out of the ordinary for him. I’d guess this performance is a good sign for him, but I wouldn’t expect him to do this every weekend this year. Even if this is his best result of the season, and the rest of his races fall between this performance and his median from last year, that would represent an enormous jump.

There was plenty of excitement about Alex Harvey’s 5th place, particularly on this side of the Atlantic. In contrast with Olsson and Halfvarsson, though, this result doesn’t look nearly as extreme for Harvey. If anything, I’d call this a strong race, but not at the outer limits of what he’s shown before. That’s why I’m taking Alex Harvey very seriously this season. Read more

New Statistical Skier Features

I’ll have a post up on Wednesday with some items from this weekends World Cup races. But I’ve been busy over the off-season and the site has seen some fairly major changes, so I need to take a second to describe what’s new.

First, some general housekeeping. Regular readers may notice that I’m going to keep to a rigid posting schedule this winter of Mon-Wed-Fri (hopefully, this will appease the haters). There are several reasons for this, but mostly I’m just a lot busier. I’m working full-time instead of part-time and the Statistical Wife and I are expecting our first kid any week now. So, I’m going to have my hands full this winter!

Second, I need to acknowledge the enormous contribution that Brayton Osgood, (former professional ski racer, current Dartmouth College DTeam coach, all around great guy)  has made to this site. I haven’t mentioned his presence here before, but he’s been invaluable in much of the behind the scenes web stuff. While I’m ultimately responsible for all the content on the site, Brayton has also been an important sounding board while I’m writing posts and analyzing data. I get the lion’s share of the attention for this site, but Brayton is very much a part of the Statistical Skier team. Credit where credit is due.

Ok…here’s what new:

User Generated Graphs

There’s a link above the tabs to data.statisticalskier.com (or at least there should be; the PHP was acting odd this weekend. If you don’t see it, try clearing your cache). This was by far the biggest project, and allows you guys to generate some of the basic types of graphs I use on the site. There is a FAQ tab on that page that runs through some of the basics, but hopefully the forms should be fairly self explanatory.

Please keep in mind that this page is still in beta! It might be slow, it might not work at all at times. We’ll be continuing to work on it, so hopefully it will get more polished and stable over time.

Head over there and have fun playing around!

Power Rankings

I know, I know. Not another points system for ranking athletes.

But if you think about the tools we have now, they are all percent back based systems like FIS points and they’re either a little too specific (FIS points for a specific race) or too general (FIS points profile from the entire past year). What I’d like to see is something more akin to ESPN’s Power Rankings for baseball, that captures who’s hot right now. So I went about building it.

My starting point was a basic ELO system, like what is widely used in the chess world. It’s based on the idea that the best way to compare performance is to use individual head-to-head match-ups between two skiers. The general idea is that everyone starts with a big pile of points. Let’s be concrete and think of them as a pile of stones. If you ski in a race, that constitutes multiple ‘matches’ against all the other skiers in that race. Each skier that beats you takes a few stones from your pile and adds them to their pile. Similarly, you take a few stones from each pile of the skiers that you beat. The number of stones that changes hands is weighted according the time gap between the two skiers and the relative size of skier’s piles of stones. There are several other minor tweaks and adjustments, but that’s the basic idea.

This is trickier to implement than it may seem. It’s a little finicky and can be sensitive to fairly arbitrary decisions about how much weight to apply to various components. But I think I’ve got it working fairly well, so we’ll give it a shot. The idea here is that this is not a serious performance measure, but a fun one. You know, the sort of thing you argue about with your coworkers at the water cooler. So don’t take it too seriously.

The current top ten ranking will always be in the tabs in the right sidebar. The distance rankings have been updated to include this weekend’s World Cup opener. (These Power Rankings use the points from the close of the previous season as a starting point.) Each discipline lists two values, the change in rank from last week and the change in their score. Keep in mind that these scores have no units. They just represent ‘the number of stones in someone’s pile’. I’ll be updating these Power Rankings more or less weekly (following the WC schedule), and I may write a post or two talking about any interesting movement they show.

If you’re at all familiar with ELO ranking systems, you may be aware that one of their limitations is that they assume a reasonably ‘well-mixed’ population. What that means is that it assumes that everyone is racing against everyone else fairly regularly. So the World Cup circuit is a reasonable group to apply this to, since it consists of a mostly fixed group of skiers competing against each other regularly. I have tinkered with extending this to all races, but it performs poorly. As you might imagine, the North American and European racing communities are not always very well mixed, so you end up with some pretty wild behavior.

Race Snapshots

I feel like people really liked the race snapshot graphs I made last season, but there were just too many of them, and they cluttered up the main page and the RSS feed. So the race snapshot graphs will all be found on a separate page (see the tab above) and will not appear in any RSS feeds. Moving these of the front page, and dialing things back to three posts a week should keep the content here more manageable and focused (and hopefully, higher quality).

Anyway, that’s what Brayton and I have been working on all summer. Enjoy!

Race Snapshot: Sjusjoen 10/15km Freestyle

Surprising races from Calle Halfvarsson and Kikkan Randall!

Canadian Ski Team: 2011-2012 Preview

A quick look at our lovely neighbors to the north!

I’m going to focus on the folks on the World Cup squad, starting with the men:

These are the WC level distance results (excluding Len Valjas). I confess I’m a little worried about Ivan Babikov, who had a rough season last year. His trend over the past four seasons appears to be headed in the wrong direction (albeit very slightly); we’ll see if he can rebound for some strong freestyle results this year.

Alex Harvey had an interesting season last year, and he’s still quite young. Given his age and how competitive he seemed in distance races last year at times, he’s the North American skier I’m most excited about at the moment. (Yes, even more than Kikkan Randall.)

Devon Kershaw also had a strong season last year, particularly in the Tour de Ski. One thing I wonder about is how well he’s been able to figure out travelling back and forth to Europe. My only reason for saying that is the odd ‘clustering’ effect you can see in the last three seasons of his distance results. They each show two distinct groups of results, one very strong cluster and one more mediocre cluster. For instance, last year he seemed to fade into March. What I’m keeping my eye on with him is consistency, then. Can he sustain those top level results through an entire season?

The women are more focused on sprinting: Read more

USST 2011-2012 Preview

Another season is just around the corner! While the USST saw some changes over the off season, the folks we are most likely to see top results from are still the Big Three: Kikkan Randall, Andy Newell and Kris Freeman.

My expectations and questions for Freeman are summed up in this graph:

This shows his median (and 10th/90th percentile – errorbars) WC results by month, using standardized percent behind the median skier. Freeman has tended to see a big dropoff in January and has had inconsistent results mid-season. The differences between the months may not seem huge, since the y axis units are not something you’re used to thinking in. But keep in mind that a difference of 0.5 can easily mean the difference between 10th and 30th (or more).

So I won’t be surprised if Freeman comes out of the gate skiing fast in November, but I’ll be very curious what happens when we hit January.

As for Kikkan Randall, I think there’s probably a lot of excitement surrounding her, considering the breakthrough season she had last year. I’ve spoken before on this blog about her chances for contending for the WC sprint title, and I think she certainly will be a podium contender in every freestyle sprint she enters. But here’s a minor note of caution: Read more

Kershaw’s Volatility

A regular reader asked me over the weekend to comment on Devon Kershaw’s less than stellar opening race of the season. Specifically, he asked:

 Kershaw seems like he’s one of the most volatile skiers on the WC circuit. Is this true?

The question of how consistent (or not) various skiers are comes up fairly regularly. I think I’ve done posts on a similar topic looking at Kris Freeman. I confess that I’ve become a bit jaded on this question, since I have generally come to believe that all skiers are less consistent than people tend to think. I think we all have a general tendency to overestimate how consistent ski racers are.

It’s still an interesting question, though. I’m going to side-step it slightly and address a related concept, variability. So the following plot shows how variable Kershaw’s results have been for each season, relative to the men’s WC field. I’ve filtered this down so as to only use skiers with a reasonable number of starts per season.

There are three panels, one for each potential performance measure. The y axis measures how variable a skier’s results were over the course of that season. The Rank panel isn’t very useful, since that performance measure is too dependent on the size of the field. So instead let’s just focus on FIS points and MPB (percent behind the median skier). The blue corresponds to Kershaw while the black line shows the ‘typical’ level of variability for the men’s WC field, with the shaded areas giving a sense of the distribution across skiers.

Both FIS points and MPB seem to suggest that last season was an unpredictable one for Kershaw. Recall that both he and Harvey tired noticeably toward the end of the season, which accounts for much of the variability. Before then, though, both measures generally suggest a skier who’s results are as variable, or less, than average.

Of course, variability isn’t necessarily the same as volatility. But now we’re delving into murkier territory. What exactly are volatile results? Consider three skiers with the following sequences of FIS points:

  1. 1.01, 5.23, 1.01
  2. 20.11, 25.64, 19.44
  3. 10.12, 52.33, 11.22
Which of those sequences is more ‘volatile’? Maybe we’d argue for (3), but proportionally it’s about the same as (1). Is a change of 5 FIS points the same whether you’re starting at the top of the pack or from the middle? Is doubling your FIS points an equivalent change regardless of whether you’re starting at the top or near the middle?
I don’t have any easy answers for this, but it’s something to think about. I’ll ponder some more specific tools for measuring volatility and get back to you…

Short Post On Slovenia And Czech Republic

I had hoped to have actual racing to write about by this week, but as we all know the snow situation in Europe hasn’t been cooperating. Hopefully we’ll finally get some racing done this weekend.

In the meantime, everyone keeps writing their little nation previews. FasterSkier’s piece on Slovenia mentioned an up and coming junior with the impressive sounding name of Rok Trsan. How are his FIS points compared to future WC top ten finishers at his age?

A little better than average for distance events, not so much with the sprinting. Although at this age, particularly with sprint points, it can be hard to read much into this.

As for the Czech’s, as usual I’m more interested in the folks not named Lukas Bauer: Read more

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