Posted By:
Eric BrehmYou are correct, given that you have two cards in your set that have the same scarcity weight, you will get the same number of total points for a 10 and a 1, as you will for two 5.5's. But the fact is, in either case the average quality of your set is 5.5. Is having a 10 and a 1 better than having two 5.5's? Perhaps it is, certainly it more expensive, but your grade point average of 5.5 does give a good indication in either case of the average quality you've got. (Yes I know, you can drown in a lake of average depth 5 inches; that is the problem with averages.)
On the other hand, if there were a set consisting of four equally weighted cards, and Guy A has one 8 and is missing the other three cards, and Guy B has completed the set with four 2's, then Guy A has a GPA of 8.0 and Guy B has a GPA of 2.0. They both have overall Set Ratings of 2.0 however -- Guy A has GPA of 8.0 * 25% complete = Set Rating 2.0 and Guy B has GPA of 2.0 * 100% complete = Set Rating 2.0 also. Which guy has the better set? Guy A has better quality on the average, but he just got started, and Guy B has lower quality but he has managed to complete the set. Seems to me the two guys have done about equal jobs in putting together a quality, complete set.
Having said that, I agree that performing mathematical operations on the grades is probably a bit simplistic and perhaps misleading -- perhaps higher graded examples of the same card should get more weight in computing the GPA than lower graded examples because they are more valuable. (This is aside from the question of the card weights PSA applies to account for relative card value/scarcity between different cards, where a scarce card in 8 gets more weight than a common card in 8.) Applying another layer of weights based on the relative value/scarcity for each individual card in each grade would probably unnecessarily complicate the system. Say you were to get 5 times as much credit for a 9 as you get for an 8, because 9's are 5 times as expensive as 8's. And suppose you have two cards, one in 8 and in one 9, that each receive a weight of 5.0 for a 9 and a weight of 1.0 for an 8. Then you would get 45 points for the 9 (5 X 9) and 8 points for the 8 (1 X 8). You would have 53 total points, and your GPA would be 8.8 (53/6) rather than 8.5, if equal weights for the grades were used. I'm not sure such a scheme would lend any improvement to the current intuitive meaning of the GPA rating.