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PDGA Round Ratings and Standard Deviation Options
L_Stephens
Posted: Tuesday, August 05, 2008 1:40:45 AM

Rank: Extreme Veteran

Joined: 7/6/2008
Posts: 437
Surprisingly I've had a few conversations lately with fairly new PDGA members like myself who are really confused about how old crappy rounds can drop off.  One way is to wait a full year between the time the round is played and the last round used for your new ratings.  Another way is for that round to fall below 100 points of your current averagerating or below 2.5 standard deviations.  When you talk about Standard Deviation....people get a very blank stare on their face.  Since I kinda know a thing or two about a thing or two about this thing we call maff...I'll try to explain for my less maff speaking buddies.
I could say Standard Deviation is defined as a measurement of dispersion between numbers in a given sample...but we start seeing the silly face of confusion again...so the best way to define..as always...is by example.  Let's take some of my putrid round ratings and show some real world examples...I have 61 rated rounds on the last update...so we'll cut off the ones from last year that are just ugly..and use just the last 20 used in the last update...not the pretty ones of recent KY States glory though.

825
909
881
867
933
868
896
890
888
899
918
877
864
827
875
868
876
891
852
851

That's 20 rounds....now we need to figure out the standard deviation.  To do that all we do is get the average round rating...add them all up and divide by 20 and we get the lowly figure of 877.75.  We are going to use this figure to find out how far off each round is from the average..and then see how much each round deviates from the average.

825          (52.75)
909             31.25
881               3.25
867          (10.75)
933             55.25
868             (9.75)
896             18.25
890             12.25
888             10.25
899             21.25
918             40.25
877             (0.75)
864          (13.75)
827          (50.75)
875             (2.75)
868             (9.75)
876             (1.75)
891             13.25
852          (25.75)
851          (26.75)

You can see the figure by what each round is different  than my average round.... numbers in () are negative numbers... next thing we do is square the numbers...aka..let's raise them by the power of two...aka...let's just multiply them by themselves....this basically turns the negatives into positives....so we get:

825          (52.75)     2782.563
909             31.25     976.5625
881               3.25     10.5625
867          (10.75)     115.5625
933             55.25     3052.563
868             (9.75)     95.0625
896             18.25     333.0625
890             12.25     150.0625
888             10.25     105.0625
899             21.25     451.5625
918             40.25     1620.063
877             (0.75)     0.5625
864          (13.75)     189.0625
827          (50.75)     2575.563
875             (2.75)     7.5625
868             (9.75)     95.0625
876             (1.75)     3.0625
891             13.25     175.5625
852          (25.75)     663.0625
851          (26.75)     715.5625

Now we take the third column and add them up to get a total of 14117.75.  We take this number...and divide by 20...the number of rated rounds...and we get 705.8875.  Next we take that figure and find the square root of it since we squared everything up to get rid of negative values earlier and we come to 26.56854 which is our standard deviation....now the PDGA says they drop any round below a Standard Deviation 2.5..which means we take the 26.56854 and multiply that by 2.5 and we get:

66.42136


So....in my above example...if you tank a round and it is 66.42136 ratings points below you average....then that particular round isn't calculated into your new player rating...it is dropped.  If your Standard Deviation is above 100..then any rounds below 100 points of your average is dropped....this formula really rewards those that consistently shoot the same rated rounds...and newer golfers have higher Standard Deviations so more of their crazy scores are kept.
L_Stephens
Posted: Tuesday, August 05, 2008 1:50:43 AM

Rank: Extreme Veteran

Joined: 7/6/2008
Posts: 437
A quick side note: I'm pretty sure that the PDGA uses an Excel formula for calculating the Standard Deviation. Excel will round these numbers between steps and the outcome will be slightly off. According to my hunch...the PDGA will calculate my Standard Deviation in the above example at 68 instead of 66.42136.
chief32
Posted: Tuesday, August 05, 2008 7:43:15 AM
Rank: Veteran

Joined: 7/14/2005
Posts: 110
Location: Lebanon
What? I can spell rating.
Ben Shooner
Posted: Tuesday, August 05, 2008 9:09:02 AM

Rank: Veteran

Joined: 9/16/2003
Posts: 248
Thanks for the breakdown Lee...That's a good point that shooting consistently will shrink your standard dev and make it more likely to get those stinker rounds dropped.

Statistically, the vast majority of your rounds 'should' be within 2.5 std. devs in either direction of the mean-but my season has proven that it's possible to have them all over the place.
perica
Posted: Tuesday, August 05, 2008 9:50:38 AM

Rank: Extreme Veteran

Joined: 9/18/2005
Posts: 365
Location: Where it puts the lotion on its skin
do they drop ones that are above 2.5 std too?
2Timer
Posted: Tuesday, August 05, 2008 10:34:49 AM
Rank: Extreme Veteran

Joined: 3/30/2006
Posts: 372
Location: Ameila, Oh
I've been trying to following your steps Lee to get mine deviation, but I have ran into a hitch. 14117.75 divided by 20 doesn't come to 26.56854.
L_Stephens
Posted: Tuesday, August 05, 2008 10:47:16 AM

Rank: Extreme Veteran

Joined: 7/6/2008
Posts: 437
Thanks 2timer...I believe I left out a VERY important step...I'm having connection issues and I had to paste that several times before the forum allowed me to post so things got chopped off and I tried to fix it on the fly. You take 14117.75 and divide by 20 to get 705.8875 and then you take the square root of that...since we squared them earlier...and that's where you get the 26.56854. Sorry about the misstep.  I'll edit the original post for clarification.
DanH
Posted: Tuesday, August 05, 2008 1:53:47 PM

Rank: Extreme Veteran

Joined: 4/4/2006
Posts: 515
Location: Lebanon, OH
Ok, Lee the mathemagician. This is what I want to know: Is there any mathematical or even logical reason why the PDGA can't just run a batch nightly to update everyone's ratings? Why do they only do it every 3 months or so?
2Timer
Posted: Tuesday, August 05, 2008 2:14:44 PM
Rank: Extreme Veteran

Joined: 3/30/2006
Posts: 372
Location: Ameila, Oh
Good thinking Dan. Atleast every Monday night to show the past weekends results. And why do they even drop low ratings? It seems to me like a rich getting richer setup. It seems like you can dump alot more rounds when your rating is really high.
osu_buckeyes
Posted: Tuesday, August 05, 2008 11:37:23 PM

Rank: Regular

Joined: 4/15/2008
Posts: 58
Location: Columbus, OH
The only thing that I can think of is that they need to get official scores and ratings done. When the rating shows up the day after a tournament is it just an estimate, a lot of times it ends up changing by a few points. Not that that is an excuse by any means but it could be the reason they only do it once every few months.
L_Stephens
Posted: Wednesday, August 06, 2008 12:00:33 AM

Rank: Extreme Veteran

Joined: 7/6/2008
Posts: 437
DanH wrote:
Ok, Lee the mathemagician. This is what I want to know: Is there any mathematical or even logical reason why the PDGA can't just run a batch nightly to update everyone's ratings? Why do they only do it every 3 months or so?


Dan...I can think of one reason...they simply don't know how....but if they would listen..I would teach them how...or simply do it for them.

Let's go over some of the reasons they can't do live rating updates.  The PDGA still lives in 1990 and their TD reports are nothing but an Excel spreadsheet with some macros.  This is silly at best.  A tournament ends and the TD fills out a report and sends it in.  The stats onsite get an unofficial update and people can see a close approximation of what their real rated rounds should be.  Then they fill out the official reports and send in the money...this may be the big issue...you don't get NOTHING official until the funds are turned in.  With the way online banking works now a days....transfers to the PDGA should be done with the click of a mouse and done with the uploading of scores.  These issues need to be addressed and updated to 2008 levels of business...not 1988.

Now...on to computer stuff.  All you need to do is build a dual xeon server with about 4GB of RAM....4 10,000RPM 500GB Hardrives that are mirrored...no need to stripe.  Estimated cost is about $4k....you can stick a DONATE Paypal button on the front page and I'm sure within 30 days...members would donate enough to build said server so it would be no cost to the PDGA fundage....I've done this with my math project I do in my spare time...speaking of which...my project far exceeds the needs of hardware and software of what the PDGA would need for the next 10 years most likely.  I have 10,000 computers communicating with my array of servers about once every few hours.  Some stats are updated hourly while others are done nightly.  **project is offline due to an export violation that I'm currently working thru with The Man**

Now..if a guy can do this at his house for 10,000 people in 147 countries around the world...then the PDGA can do this for its members and do far less updating and statistical breakouts than i do in my spare time.  If the PDGA would let me I would go crazy with statistical catagories for players, TD's, courses, counties, states, and about anything you can name.  I'd have it to where you could see standard deviations in round ratings of Intermediate Women from Ohio shooting on courses in West Virginia with an SSA of >60 in the month of July.  It could all update nightly...or atleast on Mondays..when the weekend tournies are sent in.

All they really need is a person that knows their stuff to setup a database and a front end so that TD's can easily turn in their scores....money...this database can then be used to generate all kinds of relationships of data that could amaze PDGA members...and give them more value for their membership buck.

So...it isn't about cost...because you can get people to donate such a small amount of cash....it isn't about difficulty to set up...because even I can do it by myself with no help... it isn't about load on a system...because you can use cache pages and such and you put very little stress on a database...it isn't even about not having the data to do it..because I could yank tons of information out of old records in their current format.

Thus...no...their isn't a logical reason they can't update dam near instantanously.
Otterbein_discgolf
Posted: Wednesday, August 06, 2008 8:17:30 AM
Rank: Veteran

Joined: 5/1/2007
Posts: 169
I think they have a page where you can attempt to volunteer time for many different needs within the PDGA... if you can do all of that, I think you should send them a letter and let them know.
Ben Shooner
Posted: Wednesday, August 06, 2008 9:22:58 AM

Rank: Veteran

Joined: 9/16/2003
Posts: 248
I'd imagine they don't do it immediately because they simply don't have to. Plus, waiting for 3 months of results to build up makes the changes more dramatic. I'd also argue that it's kinda cool to have them all updated at the same time so that you can either gloat, or make up excuses to your buddies-and you can see your relative progress compared to other players.

zac
Posted: Saturday, August 09, 2008 10:58:10 PM
Rank: Regular

Joined: 6/18/2008
Posts: 63
there are always changes to courses and weather conditions that come into consideration when calculating round ratings, as well as other crucial information that is included in the TD report. it is easier for them to have rolling deadlines so that both the td's have a deadline to turn official reports in, AND so that members know when this will happen. i think another idea is that by calculating over a period of time gives a more accurate reading of a rating. for example, if you play your first tourney at your home course in am3, and somehow shoot an average of 940, you would then immediately be forced to play am1. giving it a couple months allows an average to form and thus more accurate ratings and rating changes. the pdga is not a business and has little staff, if td reports are rolling in every day or maybe 10 one day and 1 the next and 0 the next and 25 the next, its a bit harder to keep track and stay on top of the process, much easier when there is a deadline to get things done by. also, nothing official happens with the uploaded reports from right after the event, it is all from the td report that is checked and reviewed, not simply just posted to the database and assumed true.
2Timer
Posted: Monday, November 24, 2008 9:49:41 AM
Rank: Extreme Veteran

Joined: 3/30/2006
Posts: 372
Location: Ameila, Oh
You can look up your new rating on PDGA.com by going to member search and putting in your info.
L_Stephens
Posted: Monday, November 24, 2008 10:52:06 AM

Rank: Extreme Veteran

Joined: 7/6/2008
Posts: 437
So far I see that Alex Hollingshead is the big winner with a rating adjustment of +33 to take her to 795. Way to improve Alex!!!!! That second round at 881 at The Seal Scream....you were on fire.
Ben Shooner
Posted: Monday, November 24, 2008 11:25:53 AM

Rank: Veteran

Joined: 9/16/2003
Posts: 248
So I take it the Pig stats never made it?
L_Stephens
Posted: Monday, November 24, 2008 11:57:47 AM

Rank: Extreme Veteran

Joined: 7/6/2008
Posts: 437
Nope...guess it takes longer than 3 months to remember to mail in the paperwork.
andersab
Posted: Monday, November 24, 2008 12:29:57 PM

Rank: Elite Veteran

Joined: 5/22/2006
Posts: 692
Location: in the chains
...and pay the fees, i forgot to tell Pete to send the check. Sorry everyone, oh well
Eric Simpson
Posted: Monday, November 24, 2008 6:13:27 PM
Rank: Veteran

Joined: 8/3/2007
Posts: 138
Location: Hebron,KY
The PDGA did an adjustment one month after a ratings update earlier this year. If the check is sent in now, it could make it in time for an adjustment if they do one this time.
andersab
Posted: Monday, November 24, 2008 7:04:41 PM

Rank: Elite Veteran

Joined: 5/22/2006
Posts: 692
Location: in the chains
Pete sent the check in last week.
alexh
Posted: Monday, November 24, 2008 7:51:20 PM

Rank: Regular

Joined: 12/22/2006
Posts: 73
Location: Lebanon, OH
Thanks Lee!
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