Odds on the election. Odds as quoted by online betting sites and corresponding probablity of winning. The probabilities add up to more than one, because the sites are profit making and don't offer actuarily fair odds.
Romano Prodi (2/9), Silvio Berlusconi (11/4)
that is Prodi wins with "probability" 81.8% and
Berlusconi wins with "probability" 26.7 %
So betting suckers lose 8.5% of what they bet.
Correcting for house odds by dividing prodi/(prodi+berlusconi) gets prob prodi wins
Prodi, Romano 1.20 Berlusconi, Silvio 3.60
that is Prodi wins with "probability" 83.3%
Berlusconi wins with "probability" 27.8%
And betting suckers had better go to oddschecker because at unibet they lose 11.1% of what they bet
Probabilities corrected by dividing prodi/(prodi+berlusconi) gives prodi wins prob 75%
Looks to me like the two sites are charging the same pool of betters to different fees. Unibet explains things in Italian and seems to be charging a rather high fee for the translation.
Bestodds looks for the best odds on other sites. I think they live off of advertising. Do make it hard to beat the market though.
They have two kinds of betting with bookies and parimutual
With bookies Prodi 1/4 Berlusconi 11/4
so Prodi wins with "probability" 80% Berlusconi with "probability" 26.7%
the odds are, as promised, less unfavorable to betters than at the sites above.
The corrected probability that Prodi wins is 75 %
Parimutual they have Prodi 0.3/1 Berlusconi 3.7/1
so "probabilities" Prodi 76.92% Berlusconi 21.28% ...
hey that adds up to less than 100% so what gives ? They are both at "betfair" which seems more than fair !?!
Political betting has the same weird odds.
update: Now I understand. Betfair also takes bets on "any other" that is that someone other than Prodi or Berlusconi will be the next prime minister. any other is paying $ 48 per dollar bet. This means that, given the odds listed above, back then if Prodi or berlusconi won, the winners would take away more money than had been bet on Prodi and berlusconi, but less than had been bet on Prodi Berlusconi or any other and thus leaving some money for the relatively fair but not more than fair betfair.
current odds Prodi pays 1.21 Berlusconi 5.3 which implies corrected probabilities
(1/1.21)/(1/1.21+1/5.3) = Prodi wins with probability 81.4%. Extremely active betting is ongoing, but the odds are changing slowly.