9-hole rounds in 2024, expected score differential

[MarcellusW]

I am a high handicapper with no real interest in an official GHIN handicap.  I play with friends who are the same.  I do calculate my handicap and try to be as accurate as possible.

 

There is a change for 2024 where 9-hole rounds will be combined with your expected score for the other 9-holes and an immediate differential will be tabulated, instead of waiting to combine with the next 9-hole round.  I am trying to figure out the most accurate way to calculate the expected score.  The USGA says

The expected score is based on the average Score Differential of a player with a given Handicap Index and a normal distribution of scores

 

At first, I thought it was just adding par +the handicap strokes you get for each hole, but I don't think that's right.

I see in some countries they add par +handicap strokes +1.

Since the system is set up in a way that you usually don't play to your handicap, it seems that this should be taken into account.

 

Does anyone have any suggestions on how to do this calculation yourself?

 

 

 

[jvincent]

Since the new method is done by an algorithm we don't have access to, your best bet would be to continue with the old system of using par + handicap strokes.

 

Any guess at the algorithm is almost certainly going to be wrong and since your group is doing their own thing anyway once you are consistent within the group it should be fine.

[Hawkeye77]

I doubt anyone has access to the software/algorithm/whatever to know nor would the USGA share it.  But then again maybe someone does and the info is out there somewhere.  There’s a lengthy thread on all this, maybe there is info in there that answers your question.  

 

Your handicap isn’t real so does it matter how much “not real” it is?
 

 

[Newby]

2 hours ago, MarcellusW said:

 

I see in some countries they add par +handicap strokes +1.

 

 

 

 

Those countries which do this will be switching the the new (secret) formula come April.

[ThinkingPlus]

It involves calculus and probability theory. The exact implementation is closely held proprietary information.

[North Butte]

I think we're one generation of WHS away from dropping any remaining pretense at transparency. They'll eventually put everything in a proprietary black box...course ratings, computation of differentials and eventually even assignment of course and playing handicaps. You'll just have to use some (no doubt PITA) app to enter hole by hole scores and the app will spit out a playing handicap before each round. 

 

I'll bail out of the system before they get that far, as will the guys I play with, but that's the way I think they're heading over the next few years. 

[DaveLeeNC]

5 hours ago, MarcellusW said:

I am a high handicapper with no real interest in an official GHIN handicap.  I play with friends who are the same.  I do calculate my handicap and try to be as accurate as possible.

 

There is a change for 2024 where 9-hole rounds will be combined with your expected score for the other 9-holes and an immediate differential will be tabulated, instead of waiting to combine with the next 9-hole round.  I am trying to figure out the most accurate way to calculate the expected score.  The USGA says

The expected score is based on the average Score Differential of a player with a given Handicap Index and a normal distribution of scores

 

At first, I thought it was just adding par +the handicap strokes you get for each hole, but I don't think that's right.

I see in some countries they add par +handicap strokes +1.

Since the system is set up in a way that you usually don't play to your handicap, it seems that this should be taken into account.

 

Does anyone have any suggestions on how to do this calculation yourself?

 

 

 

If your goal is to exactly duplicate the calculated index that you would get from GHIN, you have an additional problem. You would also need to include the PCC number.  While the PCC for a given course on a given day is not a secret, it is also not always easy to find. 

 

If I was going to be keeping my own index, I would just aggregate 9 hole scores as was done prior to 2024 (and be fully aware that I was not duplicating exactly the index that I would get from GHIN). 

 

dave

[rogolf]

27 minutes ago, DaveLeeNC said:

If your goal is to exactly duplicate the calculated index that you would get from GHIN, you have an additional problem. You would also need to include the PCC number.  While the PCC for a given course on a given day is not a secret, it is also not always easy to find. 

 

If I was going to be keeping my own index, I would just aggregate 9 hole scores as was done prior to 2024 (and be fully aware that I was not duplicating exactly the index that I would get from GHIN). 

 

dave

I thought he said he wasn't interested in GHIN.  That suggests what one of my high school geometry teachers used to say, "You can do it my way, or you can do it your own ugly way!"

[Augster]

If you all do this, and you all take net par +1, your caps will be close enough to fair in your group. It may not be fair to others you may play that have GHIN handicaps, but it’ll be close, and it won’t matter if you never play anyone with a GHIN. 

[DaveLeeNC]

I have two data points here. 

 

1) My index was 10.1, my 9 hole differential was 3.8, and they added 6.5 to get my final differential. 

 

2) My index was 10.3, my 9 hole differential was 6.7, and they added 6.6 to get my final differential. 

 

FWIW. 

 

dave

 

ps. I am unlikely to shoot better than that 3.8 differential on this course (at least at my current level of play which has generated a pretty steady index the last year or so). But my posted diff was still 0.2 higher than my index at the time. 

Edited March 13 by DaveLeeNC

[iacas]

25 minutes ago, DaveLeeNC said:

I have two data points here. 

 

1) My index was 10.1, my 9 hole differential was 3.8, and they added 6.5 to get my final differential. 

 

2) My index was 10.3, my 9 hole differential was 6.7, and they added 6.6 to get my final differential. 

 

So do you believe that if you keep playing nine-hole rounds… you're going to keep seeing your handicap go up, even if the holes you play are, like the 3.8, lower than what you'd normally score?

[davep043]

I reviewed a few "expected differential" results from my club recently.  In general, the Expected Differential for 9 holes was about equal to (0.5 * HI) + (1.2 to 1.8).  For lower handicappers the "extra" was around 1.2, for 20+ handicappers the "extra" was nearer to 1.8.  This seems pretty consistent with the results @DaveLeeNC posted just above here, his Expected Differentials were about (0.5*HI) + 1.5

[DaveLeeNC]

7 hours ago, iacas said:

 

So do you believe that if you keep playing nine-hole rounds… you're going to keep seeing your handicap go up, even if the holes you play are, like the 3.8, lower than what you'd normally score?

I believe that if I took a year's worth of 18 hole scores and reposted each 18 hole score as a pair of 9 hole scores, that my average index over that period of time would be higher in the 9 hole case. 

 

dave

[davep043]

1 hour ago, DaveLeeNC said:

I believe that if I took a year's worth of 18 hole scores and reposted each 18 hole score as a pair of 9 hole scores, that my average index over that period of time would be higher in the 9 hole case. 

 

dave

I think this might be right.  A "good" nine will never be paired with another "good" 9, it will always be paired with something closer to "average".   That means the lowest scores won't be quite as low.  Since the HI is based on the lower scores, I think the HI would be slightly higher.  I don't think the difference would be huge, but I think it would be there. 

[iacas]

32 minutes ago, davep043 said:

I think this might be right.  A "good" nine will never be paired with another "good" 9, it will always be paired with something closer to "average".   That means the lowest scores won't be quite as low.  Since the HI is based on the lower scores, I think the HI would be slightly higher.  I don't think the difference would be huge, but I think it would be there. 

 

I think it might also keep going up.

[DaveLeeNC]

13 hours ago, iacas said:

 

I think it might also keep going up.

Removed as a duplicate. 

 

dave

Edited March 14 by DaveLeeNC

[DaveLeeNC]

22 hours ago, iacas said:

 

So do you believe that if you keep playing nine-hole rounds… you're going to keep seeing your handicap go up, even if the holes you play are, like the 3.8, lower than what you'd normally score?

 

I didn't understand the point that you were trying to make earlier. You are suggesting that (due to positive feedback in this system) a person's index will tend to continue to rise indefinitely. I set up a spreadsheet to model a golfer who plays 20 consecutive 18 hole rounds with a differential of 10 on each round, and then suddenly starts to post 9 hole differentials of 5 continuously. 

 

This golfer's index crosses 11 on his/her 38th round, and the system seems to converge on an index of 13.0. Interesting. 

 

dave

[bluedot]

On 3/12/2024 at 3:37 PM, MarcellusW said:

I am a high handicapper with no real interest in an official GHIN handicap.  I play with friends who are the same.  I do calculate my handicap and try to be as accurate as possible.

 

There is a change for 2024 where 9-hole rounds will be combined with your expected score for the other 9-holes and an immediate differential will be tabulated, instead of waiting to combine with the next 9-hole round.  I am trying to figure out the most accurate way to calculate the expected score.  The USGA says

The expected score is based on the average Score Differential of a player with a given Handicap Index and a normal distribution of scores

 

At first, I thought it was just adding par +the handicap strokes you get for each hole, but I don't think that's right.

I see in some countries they add par +handicap strokes +1.

Since the system is set up in a way that you usually don't play to your handicap, it seems that this should be taken into account.

 

Does anyone have any suggestions on how to do this calculation yourself?

 

 

 

I don’t think you can do the exact calculation yourself.

 

It would seem that you have two clear choices here:

 

1. Continue to use the old net par method, and just accept that it’s a different form of estimating that will differ somewhat from GHIN.

 

2. Get registered and get an actual handicap.  With all due respect, your first sentence is conflicted; you say you have no interest in an “official” index, but you then say that you try to calculate an index as accurately as possible, and you asking a question about how to do so even more accurately, and in compliance with the new WHS methods.

 

I don’t know of any downside to maintaining an actual GHIN handicap, other than the rather nominal yearly fee, and there are LOTS of good reasons to do so, including not having to deal with the question you are asking.  One that jumps to mind is a feature on the GHIN app that calculates stroke allocation for a group, even if they are playing from different tees; you might find that very helpful?
 

Even if you’re not a member of a club, public courses provide a GHIN service, and there are e-clubs as well.  It has value.

 

 

[DaveLeeNC]

54 minutes ago, DaveLeeNC said:

 

I didn't understand the point that you were trying to make earlier. You are suggesting that (due to positive feedback in this system) a person's index will tend to continue to rise indefinitely. I set up a spreadsheet to model a golfer who plays 20 consecutive 18 hole rounds with a differential of 10 on each round, and then suddenly starts to post 9 hole differentials of 5 continuously. 

 

This golfer's index crosses 11 on his/her 38th round, and the system seems to converge on an index of 13.0. Interesting. 

 

dave

 

Here is the algebra for this case of constant differentials over 9 holes. We are looking for the convergence of the equation (see @davep043 ' s earlier post - Idx is Index and Diff is the 9 hole differential that you shoot continuously)

 

Idx = Diff + Idx/2 +O (some fixed number between around 1.2 and 1.8). Solving for I we find 

 

Idx = 2*(Diff + O)

 

dave

 

 

 

 

 

 

Edited March 14 by DaveLeeNC