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Unders / Overs betting on AFL Football
(E-mail to AFL Insiders Forum from an AFL client)
Sent: Tuesday, 10 June 2003 12:35 PM
To: 'Ozmium AFL Insiders List'
Subject: Overs / Unders
Just to stir the pot a little - I would caution people
against punting on the Unders and Overs.
Background info - some bookies have a bet type where
you can choose a side to win by Under/Over 39.5 and
others have Under/Over 24.5.
I spent a couple of years trying to search for better
payouts and trying to have an opinion on the margin
but I have concluded this type of bet is just too
difficult compared with Win and Line betting.
My point is purely mathematical. An individual bookie
bets to around 104-5% on Win betting and 105.3% on
the Line, whereas it is typically 108-9% for Unders/Overs.
Less bookies bet on Unders/Overs and are split between
the 24.5 and 39.5 margin so there is less potential
for better odds by shopping around. I would estimate
you would average 103% on Win betting, 104% on Line
betting and 107% on Unders/Overs.
This puts a significant hurdle on the extra information
you would need to have to make betting on Unders/Overs
better value than betting on Win or Line, especially
given that the margins of each cross over to some
extent and your opinion on the outcome of Win or Line
versus Unders/Overs is related (ie if you think one
is good value then the other is very likely to be,
This point can be shown quite clearly when you consider
that if you bet on an Under/Over you are deciding
to avoid the option of taking a lower dividend and
covering the other portion of the margin and well
as half cover a drawn game if you had bet on the Win.
You can compute the implicit probability/dividend
on this foregone portion of the game's margin. eg
Western Bulldogs versus Hawthorn in Round 20, 2001
at odds of $2.70 for a win, $3.35 Under 39.5 and $10.50
over 39.5. By choosing Under 39.5, the break-even
probability is 1/3.35 = 0.2985, and choosing the Win
the break-even probability is 1/2.7 = 0.3704. The
difference is 0.0719, which splits up into 0.005 for
a draw (half the 100/1 probability of a draw) and
0.0669 for Over 39.5, which converts to a dividend
So that means that even though you think the market-determined
dividend of $3.35 represents good value, the fact
that you did not choose the odds of $2.70 for a win
instead means that you think the true probability
for a win over 39.5 converts to a dividend in excess
of $14.95, well over the market-determined dividend
This would only make sense if there was a strong
reason that you expected the Dogs to not win by a
large margin, which would only be true in a few special
circumstances. (Of course the Dogs won by Over 39.5
in this example.)
The same rationale can be applied to every game,
where you can determine the implied dividend for the
portion of the margin that you choose to forego. If
you are willing to forego this margin for the dividend
then fine, but at least do it knowingly.
Happy punting. D2.
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