Chase concentration: how much of a set is really three cards
Screen 3 measures the share of a set's total raw value held by its top three cards, plus a Herfindahl index. Black & White is the most concentrated seeded set at 73%; here is the method and the first results.
A sealed box is a bet on a set. Screen 3 asks how much of that bet is really a bet on one, two or three cards.
The inputs
Every card in every seeded set, valued at its blended raw market price, observed reads beating modelled ones by the site-wide rule. A set is ranked only when at least 95% of its printed cards have an observed price, so a ranking never rests on estimates. Coverage is measured against the set's printed size, not against the cards the catalog holds: a visitor's name search can import a single card from a set the catalog does not otherwise cover, and on 17 September 2026 eight such one-card sets briefly led the screen at "100%" until the rule was tightened; a set with fewer than half its printed cards imported is now left out of the screen altogether. On 13 September 2026 all sixteen seeded sets cleared that bar: 1,912 of 1,913 cards carried an observed raw price, the one exception being a Base Set card the provider does not list.
The measures
Top-3 share is the sum of the three most valuable cards divided by the sum of every card. HHI, the Herfindahl–Hirschman index borrowed from market-concentration work, is the sum of each card's squared share of set value. It runs from close to zero, value spread evenly, to one, a single card that is the entire set. The two agree most of the time; HHI is there for the cases where the top three are close and a fourth card matters.
What the first read showed
Black & White was the most concentrated seeded set at 73% top-3 share, with the secret-rare Pikachu #115 alone holding 31% of the set's value. EX Dragon Frontiers came next at 62%, with Mew ★ #101 carrying 44% on its own. Base Set, checked against a direct database query, sat at 55% top-3 share with an HHI of 0.16.
What concentration means for a box
The higher the share, the more a box of that set is a bet on pulling one to three specific cards rather than on the set. That is not good or bad. It is a shape, and the shape is what a buyer of sealed product is exposed to. The screen calls it a fragility score because a set whose value rests on one card moves when that card moves.
Where it shows up elsewhere
Each card page carries the card's own share of its set and the set's top-3 and HHI figures, next to the card's standing in the other two population screens. Three observations, no composite. A composite would be a tip.