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Non-Skating Officials => Forms => Topic started by: King of the castle on May 21, 2012, 03:34:06 pm

Title: Stats book, what does V.T.A.R. stand for?
Post by: King of the castle on May 21, 2012, 03:34:06 pm
I know its probably a stupid question!
Title: Re: Stats book, what does V.T.A.R. stand for?
Post by: theMadStatter on May 21, 2012, 03:56:05 pm
"Versus Team Average Rating"

The idea is that this score is normalized versus the team (though the method used to achieve this is not without some criticism).

Basically, you start with the number of points scored versus the number of points scored by the opponents when a given skater is on the track.

This is then divided by the number of jams the given skater is on the track to get the average +/- per jam.  If the skater's team wins (especially by a large margin) there is a good chance that all of these values will be positive for everybody on the team, but then it makes it hard to tell if skater A who gets +2 ppj is a strong player or not.

So the average ppj of all the skaters on the team is subtracted from that, so if the average is +3, skater A is then -1 (2 - 3 = -1), which indicates that they did not perform as well their teammates.


Title: Re: Stats book, what does V.T.A.R. stand for?
Post by: King of the castle on May 21, 2012, 10:03:47 pm
Thanks.
Title: Re: Stats book, what does V.T.A.R. stand for?
Post by: IvoryGretts on May 31, 2012, 12:16:26 am
This will tell you what and why. :)

http://ragecityrollergirls.invisionzone.com/index.php?/topic/2100-understanding-the-stats-sheets/
Title: Re: Stats book, what does V.T.A.R. stand for?
Post by: theMadStatter on May 31, 2012, 04:27:02 pm
Note that that description of how the "team average" part is calculated does not match how the statbook actually calculates it.

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But if the average is -1.5 (for example there were 42 jams, and the team lost by 63 points)...
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(i.e., (Final Us score - Final Them score) / Number of jam)

The statbook calculates it by taking the +/- for each skater, adding them up, and then dividing by the number of skaters.

As for why these produce different values, consider a very simple case of 4 jams, two jammers.  Jammer A skates for 3 jams, scores +5 points in each jam.  Jammer B skates once, scores -20.  So the total jammer +/- is -15 / 4 jams = -3.75.  However (+5 + -20) / 2 = -7.5.

It comes down to: "Does the 'Average' in VTAR mean 'pick a random skater by picking a random jam and using that skater in that position' or 'pick a random skater rostered for that position (regardless of how many jams they skate)'"