PSA Set Registry Calculations

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Posted By: Eric B

How are the set ratings and grade points calculated? They don't make sense. Let's use an easy set to calculate.

The N28 Baseball set has 10 cards. So if you have 5 cards graded PSA 7 and 5 cards graded PSA 8. you should have a rating of 7.50. Easy.

But set #3 finest (Mike W) has 7 PSA 8's, 2 PSA 8's, and 1 PSA 9. Seems to me that should be a grade of 8.10. But PSA has it calculated as 8.04 grade points and 8.043 set rating.

Frank Evanov has 52 possible points and has a grade of 5.30 and set rating of 5.304.

How does this even get to the hundredth's decimal place? there's a total of 100 grade points to be had with 10 cards?

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Posted By: Jerry Hrechka

Not all cards in PSA Set Registries are equal. Some cards have a higher "WEIGHT" which can range from 1 to 10. For example a common T206 would have a weight of 1, while the T206 Honus Wagner has a weight of 10. So a common PSA5 would have 5 x 1 = 5 Grade Points while a PSA2 Wagner card would have 2 X 10 = 20 Grade Points.
That's probably were the difference between your calculations and PSA's is.

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Posted By: Eric B

OK, I see that now. The card "weightings" is on a different screen. I assumed incorrectly that since all N28's are equal in population, the weighting is the same. But they give HOF's a higher weight with Anson the highest of all.

So nown, what's the difference between grade points and set rating?

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Posted By: Jerry Hrechka

Set Rating is GPA X %Complete = Set Rating. On My PSA Horrors of War Set I have a GPA of 4.55 x 61.81% Complete = Set Rating of 2.81.
If you're interested I have scans posted of all the cards in my HOW set. You can see how graphic they are in showing the "HORRORS OF WAR".

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Posted By: Eric Brehm

Just in case anyone is interested in the precise details, the Set Rating is not quite equal to the Grade Point Average (GPA) multiplied by the Percent Complete, as stated above, although it is approximately equal to that in some cases.

The calculations that PSA actually does are as follows:

-- GPA = Total Grade Points / Total Weight (your set)

-- Set Rating = Total Grade Points / Total Weight (entire set)

where.. Total Grade Points = sum of the Grade Points for all cards you have in the set
and..... Total Weight (your set) = sum of the Card Weights for all cards you have in the set
and..... Total Weight (entire set) = sum of the Card Weights for all cards in the entire set

The Grade Points you get for each card in your set is the numerical Grade of the card multiplied by the Card Weight assigned to that card by PSA. According to PSA, the Card Weights that are assigned within each set are based on the relative values of the cards in NM-MT (PSA 8) condition. So, GPA and Set Rating are weighted averages of card quality within your set, with the weights being in proportion to the relative difficulty of obtaining each card in high grade. Set Rating also takes your degree of set completion into account, since it divides by the Total Weight for the entire set, which by the way is referred to as "the divisor for this set for weighting" by PSA.

If you want to calculate Set Rating as a function of GPA, the following formula would apply:

-- Set Rating = GPA * (Total Weight (your set) / Total Weight (entire set))

Thus, if you have every card in the set, Set Rating = GPA.

This is a reasonable, though certainly not perfect, system for ranking the quality of sets, and one could imagine numerous modifications that might improve it. When I was at the National Convention last year, I attended the PSA Set Registry luncheon, and during the Q&A session several people were complaining to Joe Orlando, President of PSA, about the set rating calculations. They wanted the weighting scheme to be modified in various ways, to better reflect relative values and so on. Too late now, I would think, better to leave it as is.

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Posted By: JimB

The weighting also does not (understandably since it would be very complex) factor in condition rarity. For example, the N28 Comisky is extemely tough in high grade.
JimB