When should you buy one-half point in CBB?

dogman · 11-19-08, 02:36 PM

A followup, based on the Ganch's numbers buying 1 point would be more correct, I believe.

Ganchrow · 11-19-08, 02:54 PM

Originally posted by dogman

If you were going to buy one-half point in CBB for 10 cents at -110 odds what numbers should you buy. Using Ganchrow's half point calculator you should buy down a half point on the favorite at numbers-3 to -4 1/2, also-7.5,-8 1/2, -9 to -13 1/2,-14 1/2, -16 and -16 1/2 and buy up a half on a dog at +2 1/2 to +4,+6 1/2,+7 1/2,+8 1/2 to +13 1/2, +15 1/2 and +16. Is this correct, for example if the dog is at +6 1/2-110 you should buy to +7 -120 because Ganch's half point calc lists them at +7-120.2

Right, so that would mean that betting blindly, while the EV on the dog at 6½ would be -4.55%, the EV at 7 would be -4.48%, making it a slightly better bet EV-wise, although not outside the likely margin of error of the estimation (FYI, I plan to update by HPC in mid-January with margins of error).

Note however, that taking Kelly considerations into account, the shorter odds on the post-point buy would make the bet palpably more favorable.

I think the point to take from this is that 10¢ is right about the fair price for a half-point at most starting levels in college basketball.

N.b., if, OTOH, you believed fair value to be 50% on the dog at 6½ and you could pick it up at +110, then your EV would be 5% and your full-Kelly utility would be 0.1136%. Were you to buy a ½ point and get the dog at +7 +100, your EV would then be 4.20% and your full-Kelly utility would be 0.0883%, making point buying a strictly bad idea in this case for risk-neutral and n-Kelly bettors alike.