Saturday, October 2, 2010

Some Help from the Official Scorer?

Pekka Rinne, career:
at Home: 42-17-5, 2.21, .924, 29.12 SA/60
on Road: 20-15-4, 2.87, .897, 27.84 SA/60

Those splits certainly make one at least a bit skeptical about whether Rinne's save percentage is being accurately reported in his home rink in the Music City, and whether we can therefore rely on those numbers to accurately reflect his performance. Nashville has been one of the places suspected of a shot recording bias (for more info see Tom Awad or JLikens), which increases the probability that there may be overcounting going on in Rinne's favour.

Unfortunately, this case is not entirely clear cut, because former Predators goalie Dan Ellis doesn't have the same extreme splits. In fact, Ellis actually has a higher career save percentage on the road despite playing all but one game of his career for the same Predators team as Rinne:

Dan Ellis, career:
at Home: 18-16-5, 2.59, .910, 28.82 SA/60
on Road: 32-26-5, 2.68, .913, 30.78 SA/60

Backup goalies can sometimes have skewed numbers because of relief appearances, but even after taking out the 12 games where Ellis came in off the bench, the pattern persists:

at Home: 18-15-4, 2.57, .913, 29.58 SA/60
on Road: 30-22-4, 2.65, .916, 31.62 SA/60

This is a fairly small sample for both Rinne and Ellis, and I expect that some of the effect is simple random variance. It is likely that the .027 difference between Rinne's home and road performance has been a bit of a statistical quirk, as has his good fortune to face almost 4 fewer shots against per game than Dan Ellis while on the road, but I'm still slightly suspicious of the official scorer in Nashville. It will be interesting to see if similar results continue this season with Ellis in Tampa and Rinne expected to once again be the main man in the crease in Nashville.


Agent Orange said...

Interesting stuff CG. Being a Wings fan I've seen enough of Pekka Rinne the last 2 years (5-1-2 0.937 2.09) against the Wings and was very impressed with him in the playoffs (first 3 games anyway) so I took a quick look at his stats.

I agree with the career home/road splits as you have indicated them but I think the SA numbers actually have a pretty small impact on his overall stats.

I calculated his overall SV% assuming the road SA/60 was the actual home number. This changed his total shots

3024 -> 2941
Total GA -> 260
The GA is a hard number which there is no estimation error (obviously).

I got the following

SV%_Est = 0.9116
SV%_Act = 0.9140

So if we assume the Nashville home scorer is giving him an extra 1.27 shots per game we only get a discrepancy of 0.0024 in SV%.

0.0024 is roughly 7 goals over the course of Rinne's career (over 100 gp, GAA impact of 0.07).

This isn't enough to change my opinion of him based on the reported stats and seeing him play.

There must something else to explain the difference between his home/road splits. Maybe Nashville needs to consider using the home strategy on the road or maybe Rinne's just gets nervous on the road (one would hope not).

His stats tell me he is a above average to good starting goalie and I haven't seen anything to change them.

The Contrarian Goaltender said...

I didn't mean to imply that this was absolute proof of overcounting, or that there were no other factors involved, it's more just a thing to keep an eye on as Rinne's career progresses, given that some have suspected his team of padding stats in the past.

I don't think Rinne's played enough in the NHL yet for us to have much confidence claiming anything about him, really, at least by going off the numbers alone. I agree that team factors could easily be at work, either team strategy or simply team home/road performance. For example, I didn't look at the relative strength of the teams that Rinne and Ellis faced, that might have had some impact, especially on the shots against totals.

Agent Orange said...

I actually agree there is likely some over and undercounting going on. What I meant to convey is that the over/under counting is only a fraction of the difference in his home/away split.

I be interested to hear a prads fan's view on the difference between Rinne's home road performance.

From the bumbers he appears drastically different. Good at home. Bad on the road.

Agent Orange said...

2nd line.

I *would* be interested