u/HucknPluck

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

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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.

I'm an executive in tech but am converting to be an executive at a more traditional business and my closet for that type of style is somewhere between "vacant" and "15 yrs ago." Does anyone have recommendations for a great stylist in NYC who I can work with for a refresh for my work style?

This past week I was down in Virginia to visit one of my good friends and I contacted Josh from Overthrow to see if he had time for us to do some in-person work. I subscribed to their monthly reviews, which have been very helpful, but I met him in person at a clinic and there are things that you can obviously see in person that are harder to see on video (so for example we diagnosed my grip was a problem), so I was very keen on getting some one-on-one guidance. (For reference, I am an MA2/MA40 player).

Josh and I did 1 hour of tech disc and then 3 hours of course work on day one and then 1 hour of field work and 3 hours of course work on day two, and it was *immensely* helpful.

There's too much content over the two days for me to cover here but the biggest thing I realized is that when I have up days and down days I have often ascribed that to how I'm feeling physically, when in reality the issue has been that there are parts of my form that I was unaware of, so the days where it felt like I was doing well, my timing was correct and I was making good choices even if I didn't realize what I was doing. And those days when it felt like I was having a down day, a lot of it was just things where something about my form or timing was off but I couldn't identify what it was. Put more simply: there are a lot more choices that need to be made for each shot and I was only making a fraction of them, and was failing to adjust parts of my body to accommodate for the shot and instead was just visualizing the shot I wanted to make and hoping that my body would do the right thing.

If you happen to be down in Virginia and have the flexibility to do work with him, I strongly recommend it.

I'm trying out a few new shot types and it turns out I need a high-speed understable disc. Looking for recos!

1. I throw about 50-55mph BH (~350) to give a sense on what would be understable for me, i.e. it needs to be fairly flippy.

2. I'm open on manufacturers though I tend to run Innova with one or two Lat64 because I know the plastic the best. I don't love the higher speed MVP options which generally feel too stable for my noodle arm. Fine trying something a bit more niche too (e.g. I have an RPM disc I really like)