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Ken Darcovich
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Joined: 14 Jun 1999
Posts: 2613
Location: Ottawa

PostPosted: Wed Aug 05, 2015 1:05 pm    Post subject: Reply with quote

lissyssil wrote:

Are the far outliers of a given round significantly impacting the scratch/slope for the round?


Sometimes yes.

3 weeks ago, CF Best, Carl and Claus shot 58 and 59, and Jaime Joss was 68, Alyssha 70, total field of 9 players.

These low handicappers shooting poorly, and high handicappers shooting well made a really low slope. The low slope amplifies differentials. Just to check, I removed Carl and Claus from the data, and the slope went up significantly.

The upshot was that for example, the full data set gave Alyssha a differential near 30, the higher slope case would have put it around 22, and nudged her handicap down.

With small groups of players used to update handicaps, really flighty and highly sensitive outcomes occur.
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lissyssil
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Joined: 28 May 2010
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Location: Aylmer, QC

PostPosted: Wed Aug 05, 2015 1:16 pm    Post subject: Reply with quote

NVM, I'll take this offline now.
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Last edited by lissyssil on Wed Aug 05, 2015 1:17 pm; edited 1 time in total
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bbp
King Geoffrey


Joined: 08 Dec 2013
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PostPosted: Thu Aug 06, 2015 7:55 am    Post subject: Reply with quote

I like reading these stat discussions.
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Ken Darcovich
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Joined: 14 Jun 1999
Posts: 2613
Location: Ottawa

PostPosted: Fri Aug 07, 2015 12:50 pm    Post subject: Reply with quote

update:

After trying a number of new things with the spreadsheet, and also, thanks to
Mark pointing out to me a page where Paul completely explained how he
calculated handicaps (which I was not even aware of....), I have updated
the spreadsheet to not include adjusted differentials which are outside of
1.4 standard deviations of the mean, for the scratch and slope determinations.

The effect of outliers, especially for small data sets, really makes a difference.


If it's ok with everyone, I will complete the season updates using the updated
and modified calculations
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Jme198
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Joined: 06 May 2012
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PostPosted: Fri Aug 07, 2015 1:05 pm    Post subject: Reply with quote

I'm curious would you mind posting a before and after table to show how the changes effect the outcome?
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Ken Darcovich
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PostPosted: Fri Aug 07, 2015 1:26 pm    Post subject: Reply with quote

To give an example, I tested this with the Toss 12 data.

With 9 of 9 data points used, a slope of 65 was determined.

With two outliers removed, a slope of 107 was determined.

so if the differential in the first case was 10, it would change to:

10 x 65/107 ~ = 6

That's a big difference.
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lissyssil
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Joined: 28 May 2010
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Location: Aylmer, QC

PostPosted: Fri Aug 07, 2015 2:15 pm    Post subject: Reply with quote

Ken Darcovich wrote:
To give an example, I tested this with the Toss 12 data.

With 9 of 9 data points used, a slope of 65 was determined.

With two outliers removed, a slope of 107 was determined.

so if the differential in the first case was 10, it would change to:

10 x 65/107 ~ = 6

That's a big difference.


With 20 rated rounds, assuming that round is used in your handicap calculation, it would reduce your handicap by 0.4, vs. recording that round as a 10 differential.

So, yes, big difference.

Also, note that TOSS 12 is an extreme example of how things would change by removing outliers. My guess would be that you wouldn't see that big a difference from events with higher turnout, or more "normal" play.
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lissyssil
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Location: Aylmer, QC

PostPosted: Fri Aug 07, 2015 3:00 pm    Post subject: Reply with quote

For TOSS 13, at the Pytel Farm, by removing the outliers from the scratch/slope calculations, the change in handicap from the posted handicap change for that week would be (assuming all players have 20 rated rounds):

Adams, Mike 0.077102428
Atos, Mark 0.112608815
Darcovich, Ken -0.01758127
Hale, Rob 0.124444277
Joss, Jamie 0.124444277
Lavino, Allysha 0.325647134
Pytel, John 0.100773352
Reitlingshoefer, Claus -0.053087656
Seguin, Serge -0.005745807
Vallee, Andrew -0.088594043
Visser, Carl -0.100429505
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lissyssil
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Location: Aylmer, QC

PostPosted: Fri Aug 07, 2015 3:15 pm    Post subject: Reply with quote

As expected, with a larger field, like TOSS 5, at Phillips Screw Driver DGC, here are the adjustments as described above:

Adams, Mike -0.034587536
Atos, Mark -0.027407177
Clavel, Stephanie -0.084850055
Darcovich, Ken 0.030035701
Hale, Rob -0.048948256
Joss, Jamie -0.099210774
Kilpatrick, Shane -0.005866097
King, Jason -0.113571493
Lariviere, Jeff -0.005866097
Lepack, Jason -0.070489335
Meldrum, Jeff 0.044396421
Penton, Geoff -0.027407177
Philips, Dan 0.044396421
Pike, Steve 0.05157678
Reitlingshoefer, Claus 0.015674982
Seguin, Serge -0.056128616
Svetkoff, Ben -0.034587536
Vallee, Andrew -0.005866097
Visser, Carl 0.008494622
Weirdsma, Alex -0.020226817
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