Old vs. New 9 Hole Posting Rules

[DaveLeeNC]

I now have enough rounds to analyze the effect of the new 9 hole posting rules (vs. the old ones where you combined 9 hole scores).  I have 55 total scores where 24 of them are 9 hole scores. The 9 hole scores are all at the same course and the 18 hole scores are spread across the 9 courses at Pinehurst Resort and CC.

 

So using the 2024 rules for all 2024 scores my average index is 10.7 with a range of 9.5 to 12.1. Using the 2023 rules of combining 9 hole scores the average index is 9.9 with a range of 8.9 to 11.6. So the impact (FOR ME!!!) is a bit under one stroke which is surprisingly close to the simulation that I did some months ago (IIRC).

 

I guess this will generate a bunch more discussion that will be a repeat of earlier discussions, but since this is actual data it seems worth posting.

 

dave

[Pnwpingi210]

1 hour ago, DaveLeeNC said:

I now have enough rounds to analyze the effect of the new 9 hole posting rules (vs. the old ones where you combined 9 hole scores).  I have 55 total scores where 24 of them are 9 hole scores. The 9 hole scores are all at the same course and the 18 hole scores are spread across the 9 courses at Pinehurst Resort and CC.

 

So using the 2024 rules for all 2024 scores my average index is 10.7 with a range of 9.5 to 12.1. Using the 2023 rules of combining 9 hole scores the average index is 9.9 with a range of 8.9 to 11.6. So the impact (FOR ME!!!) is a bit under one stroke which is surprisingly close to the simulation that I did some months ago (IIRC).

 

I guess this will generate a bunch more discussion that will be a repeat of earlier discussions, but since this is actual data it seems worth posting.

 

dave

This seems reasonable.

 

To further this discussion do you have a way to quickly to determine what you index is for

The 24 9 hole rounds (no 18 hole scores included)

The 31 18 hole rounds (no 9 hole scores included)

 

I ask as I wonder if the 2024 method brought you 9 hole index closer or farther apart from your 18 hole index.

[DaveLeeNC]

43 minutes ago, Pnwpingi210 said:

This seems reasonable.

 

To further this discussion do you have a way to quickly to determine what you index is for

The 24 9 hole rounds (no 18 hole scores included)

The 31 18 hole rounds (no 9 hole scores included)

 

I ask as I wonder if the 2024 method brought you 9 hole index closer or farther apart from your 18 hole index.

I will be doing that but not until I have 40 9 hole scores so I can generate a (2023 style) index using 8 of 20 scores.

 

dave

[iacas]

5 hours ago, DaveLeeNC said:

I now have enough rounds to analyze the effect of the new 9 hole posting rules

 

You have over 300 million rounds worth of data?! WOW! 😮 I kid, I kid…

 

I don't know that I'd call even 12 rounds (24 rounds of nine) statistically significant. And, also, while you've demonstrated that your index is a little bit different, you don't really know which is more "accurate."

This still won't answer that question fully, but it'll nudge it in that direction: what's your index (and the range) if you look at just the last 20 full 18-hole rounds?

 

Edited October 16, 2024 by iacas
emoji

[DaveLeeNC]

16 hours ago, iacas said:

This still won't answer that question fully, but it'll nudge it in that direction: what's your index (and the range) if you look at just the last 20 full 18-hole rounds?

 

I will take a look but it will have to wait for later today (stuff going on today). FWIW, this analysis is not about 'more accurate' but about the difference between 2023 and 2024 WRT 9 hole scores.

 

dave

[iacas]

17 minutes ago, DaveLeeNC said:

I will take a look but it will have to wait for later today (stuff going on today). FWIW, this analysis is not about 'more accurate' but about the difference between 2023 and 2024 WRT 9 hole scores.

 

It's never been pitched as "there won't be a difference." The issue is whether the change leads to an increase in accuracy.

 

This topic has mostly been people arguing "oh man, it takes me 2.1 differential for the front nine, which if I repeated it on the back would be a 4.2 or so, and turns it into a 5.9!" And other people arguing "you probably weren't going to shoot a 2.1 on the back nine, too, and so the USGA/R&A/WHS feel like this is a more accurate way to achieve the benefits they listed."

 

So the fact that there's a difference is beside the point. It's been known there'd be a difference, obviously, and that's one of the reasons for the change.

 

And… A few rounds by one person is still a very, very small sample size. The exact order of even two scores could have a huge effect on your range and index.

 

Edited October 17, 2024 by iacas

[DaveLeeNC]

On 10/16/2024 at 3:01 PM, iacas said:

This still won't answer that question fully, but it'll nudge it in that direction: what's your index (and the range) if you look at just the last 20 full 18-hole rounds?

I am not sure what "that question" (that won't be answered) is. But to answer the question asked...

 

Using just 18 hole rounds over the same time period, my average index was 10.3 (vs. 9.9 using the 2023 9 hole methodology and vs. 10.7 using the 2024 9 hole methodology). FWIW, I tend to shoot slightly better (differential based) scores on the 9 hole course vs. the 18 hole courses. Mostly it is a putting thing as the greens on the 9 hole course are slower.

 

A better way to sample (using a single golfer's data) the accuracy question would be to take a series of 18 hole scores and break them all up into 9 hole scores, virtually post them that way,  and compare the results. I don't have that data readily available, BTW.

 

dave

 

[iacas]

3 hours ago, DaveLeeNC said:

I am not sure what "that question" (that won't be answered) is.

 

The question as to which is more accurate.

 

3 hours ago, DaveLeeNC said:

Using just 18 hole rounds over the same time period, my average index was 10.3 (vs. 9.9 using the 2023 9 hole methodology and vs. 10.7 using the 2024 9 hole methodology).

 

As one would expect, it's closer to your calculated index. Because it's easier to have a lower pair of nine-hole differentials than to have a similarly low 18-hole differential.

 

3 hours ago, DaveLeeNC said:

Mostly it is a putting thing as the greens on the 9 hole course are slower.

 

So these aren't even nine-hole rounds played on the same 18-hole course? They're rounds played on a different course?

 

3 hours ago, DaveLeeNC said:

A better way to sample (using a single golfer's data) the accuracy question would be to take a series of 18 hole scores and break them all up into 9 hole scores, virtually post them that way,  and compare the results. I don't have that data readily available, BTW.

 

I disagree, because the golfer played the 18-hole rounds.

[DaveLeeNC]

1 hour ago, iacas said:

Because it's easier to have a lower pair of nine-hole differentials than to have a similarly low 18-hole differential.

 

That is interesting speculation that I don't understand. Why do  you say that?

 

1 hour ago, iacas said:

So these aren't even nine-hole rounds played on the same 18-hole course? They're rounds played on a different course?

 

The nine  holes rounds are all played at Midland CC (a 9 hole course). None of the 18 hole rounds are played at Midland CC.

 

dave

[iacas]

1 hour ago, DaveLeeNC said:

That is interesting speculation that I don't understand. Why do you say that?

 

It's not speculatio; it's just a mathematical fact.

 

Same reasons the odds of rolling a 3 on a six-sided die two times in a row is far more likely than doing it four times in a row. Which is way more than doing it six times in a row.

[Mr. Bean]

6 hours ago, DaveLeeNC said:

The nine  holes rounds are all played at Midland CC (a 9 hole course). None of the 18 hole rounds are played at Midland CC.

 

dave

 

The change in WHS for this year is based on a huge amount of data and the magnitude eliminates the effects of different courses. In your case it does not so it would be much more reliable if you took into account only rounds played on the same course.

 

As has already been pointed out, the only interesting thing will be to see if your 9-hole differentials will be closer to your 18-hole differentials, i.e. does the current calculation method give more accurate results for 9 vs 18 holes than the former.

 

Btw, is there any other reason for your project than trying to be able to say "ha, I told you this was a bad renewal" ?

[DaveLeeNC]

5 hours ago, Mr. Bean said:

 

The change in WHS for this year is based on a huge amount of data and the magnitude eliminates the effects of different courses. In your case it does not so it would be much more reliable if you took into account only rounds played on the same course.

 

As has already been pointed out, the only interesting thing will be to see if your 9-hole differentials will be closer to your 18-hole differentials, i.e. does the current calculation method give more accurate results for 9 vs 18 holes than the former.

 

Btw, is there any other reason for your project than trying to be able to say "ha, I told you this was a bad renewal" ?

 

OTOH, the data is perfect to answer the question that was on my mind which was "how much different are the two systems".

 

As to why there are two things going on - I am a numbers guy and this stuff holds an inherent fascination for me. Also I believe that this 9 hole approach skews my index over what it would be if I didn't play 9 hole golf at this same mix of courses and I would like to understand that. As you pointed out WRT the mix of courses involved, this is not particularly good data to explore that (other than giving me the answer to the question for the 2023 scenario). To do that I need a consistent mix of courses which I have in this form.

 

 

 

dave

 

ps. What is REALLY interesting about this data is that it is clear that I score better (as measured by differential generated per hole played) on the 9 hole course than I do on the 18 hole courses. However, my index goes down when I omit the scores from the course where I shoot the best. I find this interesting.

 

 

 

Edited October 18, 2024 by DaveLeeNC

[iacas]

58 minutes ago, DaveLeeNC said:

OTOH, the data is perfect to answer the question that was on my mind which was "how much different are the two systems".

 

It's not that either. It's an incredibly small sample size to compare two systems.

 

58 minutes ago, DaveLeeNC said:

As to why there are two things going on - I am a numbers guy and this stuff holds an inherent fascination for me.

 

Hmmmm.

 

58 minutes ago, DaveLeeNC said:

Also I believe that this 9 hole approach skews my index over what it would be if I didn't play 9 hole golf at this same mix of courses and I would like to understand that.

 

It's easier to get lower indexes when you combine nine-hole rounds. Again, that's more mathematical fact than something you have to "believe."

 

58 minutes ago, DaveLeeNC said:

ps. What is REALLY interesting about this data is that it is clear that I score better (as measured by differential generated per hole played) on the 9 hole course than I do on the 18 hole courses. However, my index goes down when I omit the scores from the course where I shoot the best. I find this interesting.

 

Why? Because you play best on the nine-hole course, those differentials are raised with the calculation 0.52x + 1.2 formula. That's not interesting to me because it's exactly what you'd expect to see.

 

It could be a few things, or a combo of them:

• If you played the same nine again (for 18), you'd tire and shoot more like your 18-hole differentials.
• The course suits your game.
• One of the course ratings is a little off.
• Etc.

Again, you're one guy, playing not even a variety of rounds at a variety of courses, and you're operating on a sample size that's very, very small. This doesn't show us anything that wasn't eminently predictable, nor does it get anywhere close to answering the only question that really matters, IMO: is this a more accurate system?

[Mr. Bean]

1 hour ago, DaveLeeNC said:

 

 

ps. What is REALLY interesting about this data is that it is clear that I score better (as measured by differential generated per hole played) on the 9 hole course than I do on the 18 hole courses. However, my index goes down when I omit the scores from the course where I shoot the best. I find this interesting.

 

 

I do not understand your last sentence. If you omit best rounds your index should go up compared to if those rounds are included. If not you are doing something wrong.

[iacas]

49 minutes ago, Mr. Bean said:

I do not understand your last sentence. If you omit best rounds your index should go up compared to if those rounds are included. If not you are doing something wrong.

 

His nine-hole differentials… are turned via the formula into 18-hole differentials that are higher than 2x the nine-hole differentials.

[Mr. Bean]

5 hours ago, iacas said:

 

His nine-hole differentials… are turned via the formula into 18-hole differentials that are higher than 2x the nine-hole differentials.

 

But 2x 9-hole differentials are not used anywhere in the system so how is that relevant?

[DaveLeeNC]

5 hours ago, iacas said:

 

His nine-hole differentials… are turned via the formula into 18-hole differentials that are higher than 2x the nine-hole differentials.

 

deleted and moved (I quoted the wrong post).

Edited October 18, 2024 by DaveLeeNC

[DaveLeeNC]

6 hours ago, Mr. Bean said:

I do not understand your last sentence. If you omit best rounds your index should go up compared to if those rounds are included. If not you are doing something wrong.

 

I calculated the 'average differential per hole played' and using that metric stated that "it is clear that I score better (as measured by differential generated per hole played) on the 9 hole course than I do on the 18 hole courses." But handicap indexes are not averages so not necessarily. I just found this unusual, unexpected, and interesting, but I didn't call it wrong. Suspicious maybe.

 

dave

[DaveLeeNC]

7 hours ago, iacas said:

Why? Because you play best on the nine-hole course, those differentials are raised with the calculation 0.52x + 1.2 formula. That's not interesting to me because it's exactly what you'd expect to see.

 

It could be a few things, or a combo of them:

• If you played the same nine again (for 18), you'd tire and shoot more like your 18-hole differentials.
• The course suits your game.
• One of the course ratings is a little off.
• Etc.

Again, you're one guy, playing not even a variety of rounds at a variety of courses, and you're operating on a sample size that's very, very small. This doesn't show us anything that wasn't eminently predictable, nor does it get anywhere close to answering the only question that really matters, IMO: is this a more accurate system?

 

If I were to stop playing everywhere except Midland CC and only played 18 hole rounds, my index would absolutely go down. I find the fact that when I add 9 hole scores from Midland CC to my index calculation then my index goes up to be 'interesting'.

 

But we disagree on so many things on this topic that I am bowing out at this point. I either type 19 more paragraphs or none. None sounds good to me.

 

dave

Edited October 18, 2024 by DaveLeeNC

[iacas]

While you may be interested in numbers, I don't think you really understand them.

41 minutes ago, Mr. Bean said:

But 2x 9-hole differentials are not used anywhere in the system so how is that relevant?

 

I took what he said ("I score better (as measured by differential generated per hole played) on the 9 hole course…") as saying he plays nine holes and that generates, say, a 5.0 differential (or a 0.556 differential per hole played), but in his 18-hole rounds he gets a 11.0 or something (for a 0.611 differential per hole played).

 

He wasn't super clear, but I don't think he was taking the nine-hole differentials after it was converted to an 18-hole differential… it seemed like he was comparing his nine-hole per-hole differential to his 18-hole differentials.

 

None of the very small amount of data @DaveLeeNC posted is surprising or odd. As we all know, the more holes you play, the more likely you are to score close to your average, so the shorter rounds are going to be more volatile, and since the index only cares about the best 8 of the last 20, your index will be lower playing only nine-hole rounds combined than playing 18-hole rounds. Your anti-handicap will also tend to be higher.

 

I disagree that Dave's rounds reveal much of anything, particularly since he plays different courses for his 18-hole and his nine-hole rounds. One may suit his game more so than the other, or other reasons for a difference in scores.

 

I'll also point out again that the USGA/et al. didn't make this change lightly. If they found that a 10.7 index golfer when playing 18 holes generates a 10.7 index, but when they played nine-hole rounds before and combined them it generates a lower index… then one may think that if the golfer played all 9-hole rounds they should still end up around 10.7. Which, owing to the more volatile nature of nine-hole rounds, it's conceivable that the 0.52x + 1.2 formula could do:

 

10.7 shoots a 3.9 differential for nine holes (one of their "better" rounds): 3.9 + 10.7 * 0.52 + 1.2 = 10.7.

[Mr. Bean]

20 minutes ago, DaveLeeNC said:

 

I calculated the 'average differential per hole played' and using that metric stated that "it is clear that I score better (as measured by differential generated per hole played) on the 9 hole course than I do on the 18 hole courses." But handicap indexes are not averages so not necessarily. I just found this unusual, unexpected, and interesting, but I didn't call it wrong. Suspicious maybe.

 

dave

 

It seems to me that you are comparing apples with pears. A 9-hole round does not equal an 18-hole round so your best 9-hole score may be worse than your best 18-hole score. Neither surprising nor suspicious. If your best 9-hole rounds were your best scores even in the WHS then your index would definitively go up if you omit them in your calculations.

[DaveLeeNC]

4 minutes ago, Mr. Bean said:

If your best 9-hole rounds were your best scores even in the WHS then your index would definitively go up if you omit them in your calculations.

 

How do I determine if my 9 hole scores are 'the best' among a mix of 9 and 18 hole scores?

 

dave

[Mr. Bean]

7 minutes ago, DaveLeeNC said:

 

How do I determine if my 9 hole scores are 'the best' among a mix of 9 and 18 hole scores?

 

dave

 

I do not know, it was you who mentioned best scores. But in WHS 9-hole scores are transferred into 18-hole score and then you can file them in ascending/descending order, and if you omit the best scores your index will go up.

[Archimedes65]

Similar result for me, though my gap was even wider because I was shooting scores 2-3 shots below than my current index.  So the delta between last years’ differential and this one was much wider than what you’re seeing.  I’m assuming that you were playing around your index.

 

Said it in the prior thread.  If you want an index above your actual ability, play nine hole rounds now.

[DaveLeeNC]

5 hours ago, Mr. Bean said:

 

I do not know, it was you who mentioned best scores. But in WHS 9-hole scores are transferred into 18-hole score and then you can file them in ascending/descending order, and if you omit the best scores your index will go up.

 

If we knew how to evaluate whether a given 9 hole round was better than a given 18 hole round, there would be no discussion here. All I did was was to assess aggregate level of play as average performance as measured by differentials. Of course handicap indexes are not averages, so here we are. I did not mention best scores, just where I score the best (on average) across all scores.

 

dave

[betarhoalphadelta]

@DaveLeeNC I'd love to see you run the below comparisons if you can, to remove any course issues... All entirely on the same course (or small group of courses) if that's what you normally play. 

 

• Your index based on your last (20) 18-hole rounds.
• Your index based on combining the differentials of the front nine holes of your last (40) 18-hole rounds.
• Your index based on your last (20) 18-hole rounds, using ONLY your front nine differential and adding your index*0.52+1.2 to complete these as 18-hole scores.

Obviously if the 9-hole course is significantly easier for your scoring than the 18-hole course(s) you play, it creates an issue trying to compare. Pulling that confounding variable out of the equation might give you a more compelling dataset.

[DaveLeeNC]

4 hours ago, betarhoalphadelta said:

@DaveLeeNC I'd love to see you run the below comparisons if you can, to remove any course issues... All entirely on the same course (or small group of courses) if that's what you normally play. 

 

• Your index based on your last (20) 18-hole rounds.
• Your index based on combining the differentials of the front nine holes of your last (40) 18-hole rounds.
• Your index based on your last (20) 18-hole rounds, using ONLY your front nine differential and adding your index*0.52+1.2 to complete these as 18-hole scores.

Obviously if the 9-hole course is significantly easier for your scoring than the 18-hole course(s) you play, it creates an issue trying to compare. Pulling that confounding variable out of the equation might give you a more compelling dataset.

 

Re: My previous post in this thread with the pic of a stack of scorecards

 

Yeah, I could do some very interesting analysis with 9 hole data derived from 18 hole rounds. But as I stated previously I have not been capturing that data in my spreadsheet. I have some of it in scorecard form but (stupid me) many of the cards that I have saved are not dated. So I would have to wade back through my GHIN emails to find the dates of those rounds (like I said - stupid me). And I believe that this matters because there is definitely some serial correlation in that data.

 

Still it is the kind of stuff that I find interesting (even though in qualitative terms I already know the answer). OTOH, if I were to post that analysis I would inevitably get some responses that I would find extremely irritating. So ......

 

dave