r/discgolf

The old rule of thumb of UDisc * 2 + 500 was convenient and would result in me trying to consistently break 200 on UDisc since I am a low-900's player, but after tracking my PDGA tournaments on UDisc this year, I've discovered that this tends to be a systematic understatement of actual PDGA ratings.

I decided to do a few statistical analyses to discover what a more appropriate conversion might be, and while it's not as convenient on the mental math, it will probably work better for you if you care about accuracy.

If you don't care about reading the rest, the formula I recommend is:
PDGA = 1.445 x UDiscRating + 633.7

(Caveat, this is only based on about 25 rounds and I have no rounds in the 1000s so this is certainly not exact, but it has a solid r2 = 0.8131 vs the old rule which had a negative r2 value so it is going to be closer than the old rule. If you want to get even closer, look below for an additional adjustment for layout difficulty)

Summary: How do these measures actually relate, when we look at the statistical tests?

1. UDisc ratings have stayed consistent

Over time, UDisc ratings have stayed pretty consistent, so it's not that there has been "deflation" on UDisc nor has there been inflation on PDGA (at least not in recent history, AFAICT). So the issue has to be with the conversion.

2. Different Parts of the Scale Behave Differently

The old rule of thumb assumed a slope of 2.0 (PDGA = 2 x UDiscRating + 500). Because the old formula subtracted 2 PDGA points for every 1 UDisc point drop, it over-penalized lower UDisc ratings:

• Lower Tier (<170) 161.7 should yield 861.7, but this formula yields 823.3 [-38.4 pts]
• Mid Tier (170–190) 180.6 should yield 890.2 but this formula yields 861.2 [-29.0 pts]
• High Tier (>190) 203.2 should yield 924.4 but this formula yields 906.4 [-18.0 pts]

So for Higher Tier (>190 UDisc) scores: The old formula is closer (+18 pt gap) but for Lower Tier (<170 UDisc): The old formula drops the predicted PDGA rating twice as fast as your actual performance drops. I suspect the misaligned slope would also create the reverse problem for very highly rated rounds.

A better slope is 1.445 and a better intercept is 633.7

3. Tournament Course Difficulty (SSA vs. Layout Par)

The second reason lower/mid-tier rounds show such high PDGA ratings relative to UDisc is how the two systems evaluate course difficulty:

• UDisc rates performance relative to fixed layout par and standard user distributions, so each stroke difference yields the same penalty despite layout difficulty.
• PDGA rates performance relative to official tournament Scratch Scoring Average (SSA) calculated from the actual tournament field on that day.

So, on tough, long tournament layouts, UDisc systematically over punishes by about -9.22 PDGA points and on normal/standard/short layouts it under-penalizes by about +6.92 PDGA points.

So if you wanted to be really rigorous, you could adjust the UDisc conversion based on layout by including those differences in the formula to produce:

• Short/Normal Layout -> PDGA Rating = 1.445 x UDisc Rating + 640.6
• Long/Difficult Layout -> PDGA Rating = 1.445 x UDisc Rating + 624.5

****************

Details for nerds (feel free to ignore, non-stats fam):

1. "How did you determine that UDisc ratings were consistent?"

(a) I did a direct comparison on the same layouts of several courses and they were nearly identical

(b) I fit a Fixed-Effects Model on 108 rounds across multi-year layouts: UDisc_Rating = Layout_FE + βscore * Score_to_Par + βtime * Time_in_Years

This yielded:

• Time Drift Coefficient (βtime​): +0.75 UDisc points/year (p=0.652).
• Score Coefficient (βscore): −5.86 UDisc points per stroke relative to par (p<0.0001)
• .

2. "How did you determine the new formula?"

(a) I did both OLS and Deming / ODR to see which performed better. The formula above had an r2 = 0.8131 which is strong.

(b) Just to make sure, I also ran a linearity and AIC test to see if it was potentially non-linear but found:

• Linear Model AIC: 174.82 (Better Fit)
• Quadratic Model AIC: 175.91 (Worse Fit)
• Quadratic term p-value: p=0.3835 (Not at all statistically significant)

.

3. "How did you determine the layout difference?"

I ran a Layout SSA Generalization Test (using One-Way ANOVA), grouping layouts into Longs/Tough vs Shorts/Standard. Results:

• F=8.924 , p=0.0076 (Statistically significant at p<0.01).
• Longs / Tough Layouts: Mean Residual = +6.92 PDGA pts (Systematic boost).
• Shorts / Standard Layouts: Mean Residual = −9.22 PDGA pts (Systematic penalty)
• .

4. "What are the shortcomings of your analysis?"

With more data points and more data from the higher-end performance area this would be much more robust, but if you're looking for something fast, this is going to be a lot better than the old rule of thumb, so it's a step-forward, even if it's not a slam dunk for now.

.

5. "...why did you do this?"

I am a Professor and my school year hasn't started so I have some free time (and am a nerd who loves disc golf). You may have seen my previous strategic analysis of the disc golf market here.

Thank you in advance, I've asked this in the past for other places that I've visited and have always enjoyed playing the suggested courses.

Anyone else experience a terribly slow response from gottagothrow to issues with an order contacting via email?

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Any suggestions?

I can’t even take credit for this one, but my friend who doesn’t even watch said it and I laughed.

Please don’t be my top rated comment

EDIT: This is now my top post of all time. Fuck

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Is it really such a hot take to say that half the pro tour events should be doubles? Is it really a crazy question to ask why the Pro Tour is so committed to singles?

From the on-field drama of all the long-range makes, to the off-field drama of who is pairing with who at each event, the entertainment value is way higher in doubles. Plus singles for men has gotten a bit stale lately; Gannon wins again... whoop-de-doo.

I'm proposing 50/50. Singles and doubles should each have four majors, a US Championship, a European Championship, and a Worlds. That's 14 hype events. Good for the sport, good for the viewers.

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Looking for some advice from other course owners, clubs, or players.

Our local course has gotten absolutely terrible with ticks and chiggers lately. You can barely walk through some of the rough without picking them up, and it's becoming a real problem for people playing and maintaining the course.

For those of you who have dealt with this:

What actually worked for your course?

Did you treat the rough/grass with anything?

Have you used a professional pest control service?

Are there certain types of mowing or vegetation management that helped?

Anything we should absolutely avoid doing?

Is there a long-term solution, or is this just something we have to deal with seasonally?

We're trying to figure out the best way to make the course safer for players without unnecessarily harming the course or surrounding environment.

Any advice from clubs that have dealt with this would be greatly appreciated.

Player with under 50 rounds played and average +11 per course. What have you learned/ figured out newer players need to know or a mind set going in?

Edit: Thanks for all the replies and taking the time to give some advice! Love this community!