The nuts,
I totally understand your 4.55 hold on -110 sides with point spreads. But I think you are losing me on your calculation system.
This is the way I figured 6.6% hold for the books:
The midway point of 400 & 525 is 463. I think it is safe to assume that if you play the game 563 times, the dog wins 100 games and the favorite wins 463. This is only an assumption and can never be proven.
Assume the book has balanced action on both the favorite and the dog. They have $10,000 on the dog and $10,000 on the favorite.
Each time the favorite wins, the book pays $1,904 to the people who bet the favorite and keep the money that was bet on the underdog. So they make a profit of $8,096 with each favorite win.
Each time the dog wins, the book keeps the $10,000 that was bet on the favorite but they pay out $40,000 to the people who bet the dog. So, when the dog wins, the books lose $30,000.
If my percentages are correct, we should have a total of 5.63 events. The favorites will win 4.63 of those contests and on those 4.63 contests the book would clear ($8,096 X 4.63) or $37,484. Then, there is the game that is won by the underdog that costs the book $30,000. So after 5.63 games, the book has held $7,484 on $112,600 ($20,000 X 5.63) worth of action, which is 6.6%.
If you move the expected win percentage up for the dog, such that we will see upsets at a rate of 1:4, then the hold for the books drops to 2.4%. If you move the expected win percentage down for the dog, such that we will see upsets at a rate of 1:5.25, the the hold for the books increases to 10%.
Very confusing stuff for me.
But I don't understand the logic behind your calculation. I'm sure it is there but I am not smart enough to see it.
Later,
Books Worst Enemy