American
Here you will see either a plus sign or a minus sign followed by a three digit number. If there is a plus sign, that means that if you bet one hundred dollars, you will profit whatever is after the plus sign. For example, +105 means if you bet $100 and you are right, you will profit $105 to have $205. If there is a minus sign, it means you have to bet whatever is after the minus sign to profit one hundred dollars. For example, -120 means if you bet $120, you will profit $100 to have $220 total. No matter what the odds are, if you are wrong, you will lose your bet.
Decimal
This is my favorite form. Here the decimal means you will have this much if you are right including what you bet if you bet a dollar. For example, 3.2 means if you bet $1 and you are right, you will profit $2.20 to have $3.20.
Fractional
Here you will see two numbers separated by a slash. If you bet the second number and are right, you will get the first number. For example, 10/11 means that if you bet $11 and are right, you will profit $10 to have $21.
Each line implies certain odds of an event occurring. However, sports books try to make a profit, so the odds they offer aren't quite fair. If the odds they offer on something are off enough that placing a bet has positive expected value, all the rich guys who devote themselves to sports betting would bet huge amounts of money on that side. There are two ways sports books protect themselves from that. Way one, get guys who really know their stuff to set the odds. Way two, offer bad prices on everything.
Let's compare pinnaclesports.com to sportsbook.com. Pinnacle Sports has a decimal price of 2.68 for the Houston Astros moneyline tomorrow (moneyline means you're betting on them to win rather than betting on them to beat the spread). Sports Book has a price of 2.65 - you stand to profit less if you are right from betting at Sports Book. So Sports Book thinks Houston is more likely to win than Pinnacle Sports does, right? And they're going to give a better price for betting on their opponent Atlanta than Pinnacle Sports does, right? Wrong! Pinnacle Sports has a price of 1.559 for Atlanta, while at Sports Book, it's 1.53. You see, Pinnacle Sports follows way one, while Sports Book follows way two. You will see especially bad prices at Sports Book or similar sites for futures with a lot of choices, like who is going to win a championship before the season starts.
Unsure Ursella: Hey Knowshon, before the NBA playoffs started, Sports Book said the Bulls were most likely to win the East, while Pinnacle said the Heat were. Should I take the average of the odds to determine who is actually most likely?
Knowledgeable Knowshon: No way! Just look at the Pinnacle Odds. Only doufuses bet at Sports Book since they have bad prices. There are no hot shots who go there to make significant moves on the lines.
Finally, I'll show you how to find the implied percentages of winning from decimal prices using R. Here is a function I wrote called oddsFinderDec. If you put in a vector with the decimal prices, it will return the implied percentages of those events occurring from those prices.
oddsFinderDec=function(vec){
goodBetOdds=1-(vec-1)/vec;
estOdds=goodBetOdds/sum(goodBetOdds);
return(estOdds)}
I'll show you an example. In tomorrow's Starcraft 2 matches, oGs is playing startale. oGs's price at Pinnacle is 1.8, while startale's price is 2.07.
In R, I would type:
oddsFinderDec(c(1.8,2.07))
and it would return:
0.5348837 0.4651163
which means oGs has about a 53.5% chance of winning.
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