I wanted to share a big research project I've been working on with the collector community. I've been thinking for some time for a way to test a commonly held theory in the Hobby: that PSA grades some cards more harshly than others, in a way that negatively impacts average collectors.
Recently my buddy and I came up with a method to test this. We use the 9:10 ratio of a card, which is the number of 9's divided into the number of 10's as graded by PSA. The rationale is that both a 9 and a 10 are mint grades. It's often very difficult to tell a 9 and a 10 apart and it's hard to argue with PSA's decision either way. The heart of this is: when PSA has a mint card in front of them, how often do they give that card a 9 vs a 10? (And is this rate different if it's a key card vs a HOF card or a common?)
The power lies in being able to compute and compare the 9:10 ratio for any card and set pretty easily. PSA has their entire population reports online so it only takes a few minutes of spreadsheet work to completely sort a set based on the 9:10 ratio. That tells us which cards in the set PSA grades the toughest, i.e. is most reluctant to give a 10.
The card that initially got me started on this was the 1980 Rickey Henderson. It has a 9:10 ratio of 81:1, which means that there are 81 times more PSA 9 grades than 10's. That's an extremely high ratio, especially when you look at the 1980 set as a whole: all the other 1980 cards average 3.3:1.
In the video I analyzed a number of key cards in the Hobby between 1978-1993...cards we are all familiar with. What I found was striking: that in each case these key cards were ranked either the toughest or one of the toughest 10's in their sets.
It's easier to watch the video, which lays it out visually.
https://youtu.be/Wirna8ihUuA