PSA Half Grade Valuation
 

Anyone ever seen anything or have an opinion on how a half grade in the PSA grading system should be calculated. Is it something like X % of the lower or higher grade? Figured I'd kick this one around with the group to see what you think.

Thanks.

I use a logarithmic function, myself.

I think a half grade value would usually be the average of the grade below and above it. If a PSA 4 was $50 and a PSA 5 was $100, I would expect a PSA 4.5 to be around $75 if the card really looks like a 4.5 grade. The only time I believe this would be different woud be for higher grades like a 9.5 when maybe a couple 10's exist but only for pre 1980 cards, or if the half grade was the highest graded. As far as percentage increases, it would be different for each type of card and also different bewteen a common and hof card.