Monday, July 27, 2009

Shooting Percentage Estimation Errors

I recently found location data for missed shots going back four years, so I decided to compare shooting percentage estimates with and without missed shots. When missed shots are included, the high shooting percentage in the slot decreases substantially in size:
We can see where the estimate error is largest by subtracting the dataset that includes misses from the one that doesn't:

So by failing to include missed shots, we've substantially overestimated the shooting percentage in the high slot, 20 to 30 feet out from the goal. We can also express the error as a percentage:

This gives a different result - shots from the blue line are much less likely to go in than we would otherwise think. If we had location data for shots that get blocked (we only know where they were blocked, not where they were shot from), we'd probably find that we're making an even larger overestimate.

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// posted by Hawerchuk @ 9:41 PM
Comments:
Doesn't the RTSS show where blocked shots came from? There is't the X,Y (by the way where did you get that?) but it would be at least something.

-Corey
# posted by Blogger the expos : July 28, 2009 7:17 AM
 
The real RTSS shows all the coordinates - I got the data from the ESPN RTSS feed. I'm not sure why the NHL gives us a version with less information in it.
# posted by Blogger Hawerchuk : July 28, 2009 8:32 AM
 
Hmm I'm on ESPN right now, I'm only getting the distance from the net.I checked the scoreboiard section and went to play by play, what am I doing wrong?

-Corey
# posted by Blogger the expos : July 28, 2009 9:32 AM
 
Don't ask me why - the data doesn't show up on the shot chart.
# posted by Blogger Hawerchuk : July 28, 2009 10:23 AM
 
Then how do you get the X,Y?
# posted by Blogger the expos : July 28, 2009 11:15 AM
 
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