New USGA 9 Hole Score Differentials Seem Way Off

[madeinguam81]

I’ll play 9 holes two or three times a week  and never liked the old system that combined two 9 hole rounds to form one 18 hole score differential. I was very happy to hear that starting in 2024, they were doing away with that system and 9 hole scores will now stand on their own (kind of).  
 

After a brief email exchange with a USGA rep, they have a proprietary formula (that won’t be shared) that will calculate an 18 hole score differential based on the number of holes played. 
 

What I’m noticing however is that the calculated differentials don’t seem accurate. Here’s a perfect example using my round today. I currently carry a 9.0 index and my course handicap for 9 holes at this course was 3. I played well and beat my course handicap and shot +2. When I posted my round, my differential was 9.6 which means that my index would trend HIGHER.  Beating my course handicap should trend my index lower, wouldn’t you think? 
 

The system just seems off. Has anyone else noticed this? 
 

 

Edited March 29 by madeinguam81

[Newby]

1 hour ago, madeinguam81 said:

I’ll play 9 holes two or three times a week  and never liked the old system that combined two 9 hole rounds to form one 18 hole score differential. I was very happy to hear that starting in 2024, they were doing away with that system and 9 hole scores will now stand on their own (kind of).  
 

After a brief email exchange with a USGA rep, they have a proprietary formula (that won’t be shared) that will calculate an 18 hole score differential based on the number of holes played. 
 

What I’m noticing however is that the calculated differentials don’t seem accurate. Here’s a perfect example using my round today. I currently carry a 9.0 index and my course handicap for 9 holes at this course was 3. I played well and beat my course handicap and shot +2. When I posted my round, my differential was 9.6 which means that my index would trend HIGHER.  Beating my course handicap should trend my index lower, wouldn’t you think? 
 

The system just seems off. Has anyone else noticed this? 
 

 

Have you taken account of the 'Average of the best 8 scores in the last 20 rounds'? 

Has a very good score been dropped from the last 20?

[madeinguam81]

21 minutes ago, Newby said:

Have you taken account of the 'Average of the best 8 scores in the last 20 rounds'? 

Has a very good score been dropped from the last 20?

Good question but I believe the differential is based on the player’s index, course rating/slope, and the secret proprietary formula (if playing fewer than 18 holes).  Handicaps update overnight so I wouldn’t think the differential calculates based on a projected handicap when the 21st score drops off. 
 

When I post, a differential is provided instantly. See screenshot. 
 

Edited March 29 by madeinguam81

[Augster]

The “extra” nine it combined with is basically you net+1. So if you were getting 4.5 shots on a side, it’ll be 5.5. Like you shot 41.5 on an “average” 9. 

[davep043]

Your "estimated differential" for 9 holes will be close to half your handicap index + 1.5.  This is something like an average 9 hole score for you, equating to about 3 over par net for 18 holes.  its going my to be just a little less for lower handicappers, a little more for high handicappers.

For you as a 9.0 index, your "average" differential for 18 is going to be something like 3 over par, or about 12.  So posting a diff of 9.6 is significantly better than your average score.  Remember, the average of your best 8 of 20 is going to be lower than the average of all 20.  Go look at your scoring record, how many scores have you posted with a differential less than 9.6?  I bet its no more than 4 of the last 20.

Edited March 29 by davep043

[Newby]

3 hours ago, madeinguam81 said:

Good question but I believe the differential is based on the player’s index, course rating/slope, and the secret proprietary formula (if playing fewer than 18 holes).  Handicaps update overnight so I wouldn’t think the differential calculates based on a projected handicap when the 21st score drops off. 
 

 

Oops. I misread your original post. For some reason I got Handicap Index in my mind rather than Differential.

However davep043 has given a very good explanation.

[madeinguam81]

29 minutes ago, davep043 said:

Your "estimated differential" for 9 holes will be close to half your handicap index + 1.5.  This is something like an average 9 hole score for you, equating to about 3 over par net for 18 holes.  its going my to be just a little less for lower handicappers, a little more for high handicappers.

For you as a 9.0 index, your "average" differential for 18 is going to be something like 3 over par, or about 12.  So posting a diff of 9.6 is significantly better than your average score.  Remember, the average of your best 8 of 20 is going to be lower than the average of all 20.  Go look at your scoring record, how many scores have you posted with a differential less than 9.6?  I bet its no more than 4 of the last 20.

this explains a lot. Thank you very much for the detail. I’ll definitely take a look but that makes a lot of sense.

[Schulzmc]

3 hours ago, davep043 said:

Your "estimated differential" for 9 holes will be close to half your handicap index + 1.5.  This is something like an average 9 hole score for you, equating to about 3 over par net for 18 holes.  its going my to be just a little less for lower handicappers, a little more for high handicappers.

For you as a 9.0 index, your "average" differential for 18 is going to be something like 3 over par, or about 12.  So posting a diff of 9.6 is significantly better than your average score.  Remember, the average of your best 8 of 20 is going to be lower than the average of all 20.  Go look at your scoring record, how many scores have you posted with a differential less than 9.6?  I bet its no more than 4 of the last 20.

 

OK - this is not making sense to me. I am not saying you are wrong. I assume you are right. I’m trying to figure out what I have wrong that is causing this to not make sense to me. 

 

Here are my eight “counting” rounds (out of my last 20) and their differentials right now:

 

82  dif 10

83  dif 9.8

80  dif 5.9

81  dif 8.2

82  dif 9

83  dif 9.8

78  dif 5.7

82  dif 9

 

If you average out those differentials you get 8.425 - which is exactly my index (8.4)

 

So if I go out tomorrow and shoot 39, that should translate into a differential of ~5.7 (which would equal my 78 I shot) and be better than my index. But the OP did that (shot a nine hole score which when doubled should have been better than his index since it was better than his average of his top 8 scores) and his was higher than his index.

 

Again - I assume I am missing something. What is it?

[Celeras]

51 minutes ago, Schulzmc said:

 

OK - this is not making sense to me. I am not saying you are wrong. I assume you are right. I’m trying to figure out what I have wrong that is causing this to not make sense to me. 

 

Here are my eight “counting” rounds (out of my last 20) and their differentials right now:

 

82  dif 10

83  dif 9.8

80  dif 5.9

81  dif 8.2

82  dif 9

83  dif 9.8

78  dif 5.7

82  dif 9

 

If you average out those differentials you get 8.425 - which is exactly my index (8.4)

 

So if I go out tomorrow and shoot 39, that should translate into a differential of ~5.7 (which would equal my 78 I shot) and be better than my index. But the OP did that (shot a nine hole score which when doubled should have been better than his index since it was better than his average of his top 8 scores) and his was higher than his index.

 

Again - I assume I am missing something. What is it?

 

I don't know the information but Dave said your 9 hole differential isn't half your handicap, it's half your handicap plus 1.5. I would guess this weighting is due to the fact that its easier/more common to play a good 9 then it is a good 18.

[Augster]

4 hours ago, Schulzmc said:

 

OK - this is not making sense to me. I am not saying you are wrong. I assume you are right. I’m trying to figure out what I have wrong that is causing this to not make sense to me. 

 

Here are my eight “counting” rounds (out of my last 20) and their differentials right now:

 

82  dif 10

83  dif 9.8

80  dif 5.9

81  dif 8.2

82  dif 9

83  dif 9.8

78  dif 5.7

82  dif 9

 

If you average out those differentials you get 8.425 - which is exactly my index (8.4)

 

So if I go out tomorrow and shoot 39, that should translate into a differential of ~5.7 (which would equal my 78 I shot) and be better than my index. But the OP did that (shot a nine hole score which when doubled should have been better than his index since it was better than his average of his top 8 scores) and his was higher than his index.

 

Again - I assume I am missing something. What is it?

The “extra 9” differential for an 8.4 would be 4.2+1.5= 5.7 PLUS the differential for the 39 you actually shot, which would give you your total differential for the round. 

[ChaosTheory]

9 hours ago, Schulzmc said:

 

OK - this is not making sense to me. I am not saying you are wrong. I assume you are right. I’m trying to figure out what I have wrong that is causing this to not make sense to me. 

 

Here are my eight “counting” rounds (out of my last 20) and their differentials right now:

 

82  dif 10

83  dif 9.8

80  dif 5.9

81  dif 8.2

82  dif 9

83  dif 9.8

78  dif 5.7

82  dif 9

 

If you average out those differentials you get 8.425 - which is exactly my index (8.4)

 

So if I go out tomorrow and shoot 39, that should translate into a differential of ~5.7 (which would equal my 78 I shot) and be better than my index. But the OP did that (shot a nine hole score which when doubled should have been better than his index since it was better than his average of his top 8 scores) and his was higher than his index.

 

Again - I assume I am missing something. What is it?

They don’t double the nine hole score.  They add an average score (differential, actually) to it (to its differential).

Your example might end up as 2.9 + 5.0 for a 7.9.  So better than your index but tempered by the fact that it was only a 9 hole round.
 

Edited March 30 by ChaosTheory

[davep043]

9 hours ago, Schulzmc said:

Again - I assume I am missing something. What is it?

Now go average ALL of your last 20 scores.  I'd bet its in the ballpark of 11 to 11.5.  So your AVERAGE differential is probably around 5.5 to 5.7 for 9 holes.  In the specific case you mention, your 39 would be about 2.85 differential, added to say 5.6 for the "expected", for an 18-hole diff of 8.4.  Remember, shooting your handicap is a dang good score, you only do it 20% of the time, approximately.  Essentially, a good 9 hole score will be nudged a little higher by the "expected diff", a poor 9 will be nudged a bit lower.  

 

9 hours ago, Celeras said:

I would guess this weighting is due to the fact that its easier/more common to play a good 9 then it is a good 18.

Its just something like "average".  And its not based on an individual player's "average", its based on average for all 8.4 index golfers, in the case of @Schulzmc.  

[Newby]

2 hours ago, davep043 said:

Its just something like "average".  And its not based on an individual player's "average", its based on average for all 8.4 index golfers, in the case of @Schulzmc.  

I haven't seen or heard anything different but have you more information (eg been given a nod)?

Edited March 30 by Newby

[nsxguy]

22 hours ago, madeinguam81 said:

I’ll play 9 holes two or three times a week  and never liked the old system that combined two 9 hole rounds to form one 18 hole score differential. I was very happy to hear that starting in 2024, they were doing away with that system and 9 hole scores will now stand on their own (kind of).  
 

After a brief email exchange with a USGA rep, they have a proprietary formula (that won’t be shared) that will calculate an 18 hole score differential based on the number of holes played. 
 

What I’m noticing however is that the calculated differentials don’t seem accurate. Here’s a perfect example using my round today. I currently carry a 9.0 index and my course handicap for 9 holes at this course was 3. I played well and beat my course handicap and shot +2. When I posted my round, my differential was 9.6 which means that my index would trend HIGHER.  Beating my course handicap should trend my index lower, wouldn’t you think? 
 

The system just seems off. Has anyone else noticed this? 
 

 

 

Not necessarily.

 

You're a 9.0 index. Total of your 8 counting rounds is 72.0 (72/8=9.0)

 

Example 1 - Consider the following 8 (of 20) counting differentials. The initial assumption here is NONE of these 8 rounds drops off your scoring record due to this latest 9.6 getting included.

 

12.0

11.0

10.0

10.0

  9.0

  8.0

  5.0

  7.0

 72.0

 

Now you shoot a score that gives a 9.6 diff, as you did.

 

The newer 9.6 kicks out the 12.0 resulting in 69.6 (new total of your 8 counting rounds); divided by 8 giving an index of 8.7. So your index goes lower even though your latest differential is higher than your index (before that round).

 

Example 2 - Now let's suppose the 7.0 above drops off as your latest 9.6 gets added in.

 

Now your total of your 8 best is 74.6. Divided by 8 = 9.325, rounded = 9.3.

 

So, in this case, your index would go up due to the 7.0 falling off and the 9.6 diff added in - giving an index higher than before that round.

 

So, same diff added in - 2 different results coming out.

[Augster]

1 hour ago, nsxguy said:

 

Not necessarily.

 

You're a 9.0 index. Total of your 8 counting rounds is 72.0 (72/8=9.0)

 

Example 1 - Consider the following 8 (of 20) counting differentials. The initial assumption here is NONE of these 8 rounds drops off your scoring record due to this latest 9.6 getting included.

 

12.0

11.0

10.0

10.0

  9.0

  8.0

  5.0

  7.0

 72.0

 

Now you shoot a score that gives a 9.6 diff, as you did.

 

The newer 9.6 kicks out the 12.0 resulting in 69.6 (new total of your 8 counting rounds); divided by 8 giving an index of 8.7. So your index goes lower even though your latest differential is higher than your index (before that round).

 

Example 2 - Now let's suppose the 7.0 above drops off as your latest 9.6 gets added in.

 

Now your total of your 8 best is 74.6. Divided by 8 = 9.325, rounded = 9.3.

 

So, in this case, your index would go up due to the 7.0 falling off and the 9.6 diff added in - giving an index higher than before that round.

 

So, same diff added in - 2 different results coming out.

Well done!

[larrybud]

4 hours ago, nsxguy said:

So, in this case, your index would go up due to the 7.0 falling off and the 9.6 diff added in - giving an index higher than before that round.

 

So, same diff added in - 2 different results coming out.

 

So many people assume that if they shoot over their handicap their handicap MUST go up, and if they shoot under their handicap, their handicap MUST go down. But it all depends on what that 21st score that you're rolling off is.

 

That said, seems like this new system will help handicappers. Take a guy who sandbags, and then posts a "good" 9 hole score. That differential will be added to what I will call a "statistical differential" that is based on the player's current handicap. Since his current handicap is BS, the new 18 hole differential will be BS, even though a "legit" 9 hole score is posted. 

Edited March 30 by larrybud

[davep043]

6 hours ago, Newby said:

I haven't seen or heard anything different but have you more information (eg been given a nod)?

I attended a handicapping workshop a couple weeks back, run by our state golf association.  That's what he said, the expected diff is based on all players of the same handicap index.  As I've said, to me the numbers I reviewed seem pretty close to what I expect for an average 9 hole differential.  But really, average diff isn't nearly as sophisticated sounding as an expected score based on a mysterious algorithm run on all players with the same index.

[Newby]

58 minutes ago, davep043 said:

I attended a handicapping workshop a couple weeks back, run by our state golf association.  That's what he said, the expected diff is based on all players of the same handicap index.  As I've said, to me the numbers I reviewed seem pretty close to what I expect for an average 9 hole differential.  But really, average diff isn't nearly as sophisticated sounding as an expected score based on a mysterious algorithm run on all players with the same index.

By coincidence I just got a note from a referee colleague who had attended an England Golf presentation (or webinar perhaps) recently, where he got the same message.

[madeinguam81]

1 hour ago, davep043 said:

I attended a handicapping workshop a couple weeks back, run by our state golf association.  That's what he said, the expected diff is based on all players of the same handicap index.  As I've said, to me the numbers I reviewed seem pretty close to what I expect for an average 9 hole differential.  But really, average diff isn't nearly as sophisticated sounding as an expected score based on a mysterious algorithm run on all players with the same index.

This makes a ton of sense, especially from an execution standpoint.  When I see “expected score” I think they’d factor how I played for the 9 holes into a calculation but that just complicates things. 

[rogolf]

Further, isn't the "expected score" based on a slope rating of 113?

[nsxguy]

On 3/29/2024 at 6:29 PM, davep043 said:

Your "estimated differential" for 9 holes will be close to half your handicap index + 1.5.  This is something like an average 9 hole score for you, equating to about 3 over par net for 18 holes.  its going my to be just a little less for lower handicappers, a little more for high handicappers.

For you as a 9.0 index, your "average" differential for 18 is going to be something like 3 over par, or about 12.  So posting a diff of 9.6 is significantly better than your average score.  Remember, the average of your best 8 of 20 is going to be lower than the average of all 20.  Go look at your scoring record, how many scores have you posted with a differential less than 9.6?  I bet its no more than 4 of the last 20.

 

Close to half + 1.5 isn't very mathematical. Neither is a little less for lower caps and a little more for higher ones. LOL

 

So basically the WHS is keeping the exact formula to themselves.

 

I thought you and Augster had nailed it with the 1/2 index + 1.5

 

It just so happens that, while the USGA didn't give us the CR and slope in their example (below), coincidentally(?) their example came out exactly right.

 

But when I apply the front diff for our OP. 3.76 + 6 (4.5+1.5) I get 9.7 or 9.6, depending on rounding, not the 9.6 GHIN came up with. "Slightly lower for lower caps" ?

 

Anyway, it looks really close at 1/2 index + 1.5 so I guess there's no real need to get further into the weeds.

 

 

 

Edited March 31 by nsxguy

[ChaosTheory]

13 hours ago, madeinguam81 said:

This makes a ton of sense, especially from an execution standpoint.  When I see “expected score” I think they’d factor how I played for the 9 holes into a calculation but that just complicates things. 

Maybe just semantics, but they do factor your play into it.  Your actual good score counted.  Except they don’t assume you’ll repeat it on a second nine.  They have decided to assume your second nine would be completely average.  By definition your average is the most likely score, odds-wise.  

Edited March 31 by ChaosTheory

[davep043]

11 hours ago, nsxguy said:

Close to half + 1.5 isn't very mathematical. Neither is a little less for lower caps and a little more for higher ones. LOL

 

So basically the WHS is keeping the exact formula to themselves.

That's right, they're not releasing the formula.  Of course, you can do just what I did, get a list of 9-hole scores from a variety of handicap levels and back-calculate the "estimated differential" for each score.  Then plot it ion a graph, you'll get a pretty straight-line relationship between HI and the "approximately 1.5" number I referenced.  From my research, its going to run from about 1.2 for near-scratch golfers to about 1.8 for 20+handicappers.  If for some reason you NEED to get more accurate, you'll NEED access to millions of scores, and the time to crunch those numbers.

11 hours ago, nsxguy said:

It just so happens that, while the USGA didn't give us the CR and slope in their example (below), coincidentally(?) their example came out exactly right.

The CR and Slope have already been used to calculate the players 9-hole differential for the holes he played, so you no longer need that information.  The Expected Differential is similarly independent from any course-related data.

12 hours ago, rogolf said:

Further, isn't the "expected score" based on a slope rating of 113?

The "magic number" is expected Differential, so this is AFTER any adjustment for CR or Slope would have been done, its independent of any course-related data..

 

[nsxguy]

4 hours ago, ChaosTheory said:

Maybe just semantics, but they do factor your play into it.  Your actual good score counted.  Except they don’t assume you’ll repeat it on a second nine.  They have decided to assume your second nine would be completely average.  By definition your average is the most likely score, odds-wise.  

 

That's the part that confused me a little bit. I initially thought that good/good, or bad/bad, would be the expectation.

 

But then, thinking about it more, I think I've had far more "average" overall scoring rounds where front and back had "large" discrepancies than I had "great" rounds where the front and back closely "matched".

 

And bad/bad ? That's even more expected, as once I've had a poor front, a bad back is far more likely to happen than a good one - not for a lack of trying but,,,,,,,,,,

 

Of course, then it likely doesn't matter as that bad/bad won't make it into my index anyway.

[nsxguy]

4 hours ago, davep043 said:

From my research, its going to run from about 1.2 for near-scratch golfers to about 1.8 for 20+handicappers.

 

After I made that previous post I stumbled upon another post of yours where you noted 1.2-1.8.

[Schulzmc]

On 3/30/2024 at 7:37 AM, davep043 said:

Now go average ALL of your last 20 scores.  I'd bet its in the ballpark of 11 to 11.5.  So your AVERAGE differential is probably around 5.5 to 5.7 for 9 holes.  In the specific case you mention, your 39 would be about 2.85 differential, added to say 5.6 for the "expected", for an 18-hole diff of 8.4.  Remember, shooting your handicap is a dang good score, you only do it 20% of the time, approximately.  Essentially, a good 9 hole score will be nudged a little higher by the "expected diff", a poor 9 will be nudged a bit lower.  

 

11 hours ago, ChaosTheory said:

Maybe just semantics, but they do factor your play into it.  Your actual good score counted.  Except they don’t assume you’ll repeat it on a second nine.  They have decided to assume your second nine would be completely average.  By definition your average is the most likely score, odds-wise.  

 

Now I get it. Thanks so much. Makes sense. 

 

6 hours ago, nsxguy said:

But then, thinking about it more, I think I've had far more "average" overall scoring rounds where front and back had "large" discrepancies than I had "great" rounds where the front and back closely "matched".

 

Yeah - as I think about it I agree. I’ve had a lot of what we call “Ray/Ray” rounds. (Ray Floyd on the front nine, Ray Charles on the back.)

 

And if I have this right if my nine hole score is much worse than normal the formula would actually give me a differential LOWER than if I had assumed an equally bad back nine.

[nsxguy]

15 minutes ago, Schulzmc said:

Yeah - as I think about it I agree. I’ve had a lot of what we call “Ray/Ray” rounds. (Ray Floyd on the front nine, Ray Charles on the back.)

 

 

Now that is just laugh-out-loud funny !!! (I scared my pet bird)

 

Never heard that one before. 👍

[Imp]

Played in excel for a sec... if it's ~1.2 for a scratch and ~1.8 for 20+, we can have a lookup that goes a little something like this and *get close but not exact*...

0	1.2
1	1.23
2	1.26
3	1.29
4	1.32
5	1.35
6	1.38
7	1.41
8	1.44
9	1.47
10	1.5
11	1.53
12	1.56
13	1.59
14	1.62
15	1.65
16	1.68
17	1.71
18	1.74
19	1.77
20	1.8

 

Its an even (linear) step value of .03 between values. Not exact, but if you do your own tracking for leagues or other purposes... it'll be more gooder.

 

Essentially, the "other 9" will be half index + lookup for differential above. If you wanted to get pedantic, you can split the .03 per every .x between the integers, ie, .003 per every tenth. It's just math, and will get you closer. 

 

 

 

Edited April 1 by Imp

[Imp]

Assumptions made with this Excel formula that doesn't catch every case (like PCC) are that:

a) 0 is a 1.2 baseline, and

b) off of 0, it can increment and decrement .003 for every tenth...

 

In a field that allows for 2 decimals: =1.2+(.003*HalfIndex)*10+HalfIndex

Another field that has the HalfIndex. 

 

Example: A1 = HalfIndex (10)

A2 has the formula above (results in 11.5 differential)

 

 

 

Edited April 2 by Imp

[szaino]

The USGA always seems to make things more complicated than they have to be. I am just speaking from many years of playing golf. This thread on GHIN is an example.

 

In simple terms a player's GHIN is an average of the differentials for a given number of scores. So why can't it be kept that simple and just be calculated on actual hole played. If you play 9 holes, then just count those holes in the calculation and it would be counted or weighed as 1/2 a round. 

 

For a 9 hole round, I am not a fan of the new rule which creates a fictitious estimate of what a player would be expected to score on the remaining holes that they never played!! It is an extra step and a superfluous exercise in mental gymnastics.