Cardboard Calculus - A Week In Review

Card prices and population counts are not the only things in the hobby growing exponentially by the day. The amount of data being generated is astounding and much of it remains untapped. This is why I have created the Instagram account Cardboard.Calculus. Almost daily I uncover a new piece of information from the vast amount of data in the hobby and this is my platform to share it with the sports card world. In this series I will take a look back at each week’s most interesting posts and provide further explanation for what I think it means for the hobby and our decision making when buying and selling cards.

Our pricing research is done using Sports Card Investor’s Market Movers data. You can sign up for your own Market Movers Subscription to access the data on your own and by using the promo code GRINDERS you will get 20% off your first payment on any subscription. You will want to sign up for Market Movers specifically in order to access the great tools and data, and if you sign up for the annual Market Movers subscription, you will save you 20% on the entire year instead of just the first month.

Cardboard Calculus – A Week In Review

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This week our analysis focuses on the importance of context. You must scrutinize everything that you watch and read in this hobby including these articles. If you take in new data and use it wisely you will gain an edge in this hobby that very few people have. If data is used incorrectly however it can be very costly. Hopefully in this article I can explain some of the ways we can make sure to not let that happen to us.

Modern Gem Rates are High but Falling

The chart above shows Topps Chrome gem rates for Lebron and Curry’s rookie years as well as each year of Prizm since it has been released. Gem Rate is the percentage of cards submitted to PSA that get a grade of 10 which they call a “Gem Mint”. As you can see there was a big jump in gem rate for the first few years of Prizm. Some of this may be explained by better manufacturing technology as well as an increased knowledge in the hobby on how to protect your cards. What is more interesting is how Gem Rates have been falling for Prizm each of the last 3 years. Maybe they have increased the speed of production at the expense of quality? Maybe PSA is being tougher on their grades to limit population sizes? To be honest I don’t really know how to explain this but it will most certainly have a ripple effect in the hobby.

Falling gem rates may be good for the modern sets as it offsets some of the rise in population growth however probably not enough to make a major difference. The more important lesson is to understand the context around each year and set before making a decision on how much to mark up highly graded cards. I would be willing to pay more for a Curry 2009 PSA 10 relative to a 9, then say a Giannis in 2013, because it is more rare relative to a 9. There is also some population growth insurance because fewer of the cards submitted for Curry’s rookie year will add to the PSA 10 population. It is also worth noting that in modern cards we tend to discount things like PSA 8s and PSA 7s but this may be a mistake if we carry it over into older sets like 80s Topps. I have a 1981 Kareem card that looks very good as a PSA 8 and has almost tripled in value since I bought it. Just look at the population breakout below. Whenever looking at data just make sure to consider the context around that data.

Winning is Half the Battle

We are going to switch gears a little outside of population counts and look at how much winning impacts card prices. For this analysis I wanted to keep as much constant as possible so I only looked at the 2017 draft class and only looked at Base PSA 10 Prizm prices. My goal was to see how much did Total Win Shares mean to the player’s price relative to his peers. The overall correlation of WIn Shares to Price was 0.56. One way to think about this is that Win Shares explained 56% of the differences in price. That is a large portion of the difference but that also means that other things make up the other 46%. These could be things like position, team market size, social media followings ect.

Despite there being a theory that the hobby is warming up to big men they still get much less love than wings and guards. Bam, Collins, and Allen are all well below the dotted line which means they are priced lower then their Total Win Shares would indicate. Now look at Mitchell, Fox, and Tatum who are all non-bigs and priced higher than their Win Shares would otherwise indicate. This does not mean that they are overpriced it just means they most likely grade out better in the things that make up the other 46%. As I gather more data I will be able to track these things over time and see how these correlations change as the players advance in their careers. At the end of the day no matter how exciting the player is winning provides more attention and hype which will work out well for their prices.

How Should I Sell?

One question many newcomers to the hobby may ask is whether or not you should sell on ebay as fixed with best offer or as an auction. The real answer to this is it depends. From the two charts above you will see recent sales prices for Luka Doncic and Jamal Murray broken out by the type of ebay listing. I was able to directly export this data from Market Movers which is just another reason why it is such a great tool for people trying to get ahead in the hobby through data. What you will notice is there is little to no difference in average sales price when looking at Luka Doncic’s Prizm PSA 10. On the flip side you look at the Jamal Murray results and auctions are consistently underperforming fixed/best offer.

I believe this is because of the difference in liquidity and market dynamics. Doncic is one of the hottest names in the hobby which means the search volumes on ebay for his stuff is much higher. You also have many more sales to build in a solid baseline price that people can reference. Murray despite being a great player is not talked about as much and his Select Silver has only a fraction of the sales volume that Luka’s Base Prizm has. Fixed/Best Offer always gives you the most control of the final sales price so if you are looking for the safest and simplest way to sell I would just list things at a fair price and allow for buyers to submit best offers and negotiate from there. If you are sitting on a card that is in high demand at that moment you can certainly roll the dice with an auction. I prefer 7 day auctions as it gives buyers more time to see and save my listing.

As always you can sign up for your own Market Movers Subscription to access the data on your own and by using the promo code GRINDERS you will get 20% off your first payment on any subscription.


All of the items we covered today express the importance of context and due diligence. Do not take any piece of data at face value but rather consider all the context around that data and adjust your decision making accordingly. Please check the links below to make decisions on your own investments into these products. I hope that you enjoyed this article and let me know what you think in the comments section below.

Sports Card Description Last Sale Price
Luka Doncic Select Scope PSA 10 Last Sale Price $4500
Luka Doncic Select Concourse Silver PSA 10 Last Sale Price $3900
Luka Doncic Select Premier Silver PSA 10 Last Sale Price $3300
Jayson Tatum Select Concourse PSA 10 Last Sale Price $370
Ja Morant Select Concourse PSA 10 Last Sale Price $339.40
Ja Morant Select Premier Level PSA 10 Last Sale Price $520
Anthony Davis Select Hot Rookies PSA 10 Last Sale Price $500
Jamal Murray Select Silver PSA 10 Last Sale Price $700

About the Author

  • Brennan Ruby (xBigtymerBx)

  • After playing DFS for over 8 years Brennan switched over entirely to sports card investing in the middle of 2019. Since converting, Brennan has bought and sold close to 100 cards on eBay. Ruby focuses his investing on long-term buy and hold opportunities, as well as short to intermediate investing such as prospecting and buying raw cards to be graded. Ruby focuses entirely on the basketball market and personally collects former Kentucky players, since his wife grew up just down the road from Lexington, and officially put him on the Wildcat bandwagon!


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