Exacta Probability and Percentage

[punteray]

At one time there was a discussion on calculating the payout for an EXACTA using probability and percentages.

I had a copy of the procedure but have misplaced it or just plain lost it.

I have tried to search the forum but have come up empty.

Can anybody help on this?

[whodoyoulike]

Originally Posted by punteray

At one time there was a discussion on calculating the payout for an EXACTA using probability and percentages.

I had a copy of the procedure but have misplaced it or just plain lost it.

I have tried to search the forum but have come up empty.

Can anybody help on this?

Exacta payouts are provided or shown on my ADW and the track and OTB provides it on their monitors before each race is run.

Are you sure it wasn't for Trifectas or a Superfecta?

[Poindexter]

Originally Posted by punteray

At one time there was a discussion on calculating the payout for an EXACTA using probability and percentages.

I had a copy of the procedure but have misplaced it or just plain lost it.

I have tried to search the forum but have come up empty.

Can anybody help on this?

If you are talking about from your own oddsline, the math is fairly simple. Say you have the 1 horse 2-1 and the 6 horse 8-1

.333333 chance the 1 wins and should he win the 6 has a .111111111/.666666666 chance of beating the rest of the field

so the chances of hitting are 1/3*1/6 or 1/18 which is a fair value of 17-1.
Actually the formula to determine the exacta price needed is much easier than that. Simply put it is :

(win odds*place odds)+win odds. So in the example I gave (2*8)+2=$18 for a $1 exacta. So the good news is you can likely do this in your head.

Now if you are using the public's line you would have to adjust for the takeout, so assuming a 15% takeout if the public had the 1) 2-1 and the 6) 8-1 the 2 becomes .33333/1.15 or .29(around 5-2) and the 8-1 becomes .1111111/1.15 or .096. More like a 9.5-1 shot. EDIT-I think my math is probably wrong on the public line.

Now all this assumes that the place line matches the win line, which is seldom the case in racing.

FWIW, I do not use this model myself even when I do line races.

[Poindexter]

Okay with the public odds if you want to convert to a fair exacta price I would convert the tote odds to odds if there were no takeout. So to do so take the total (win pool/$ bet on a horse)-1. So if a horse has $5000 out of a $15,000 pool he would be a true 2-1 shot even though his actual odds is 1.55 to 1. If another horse in the race is has $1000 to win on him he is a true 14-1 shot(even though he is a 11.75-1 on the tote board). The fair exacta price theoretically would be (2*14)+2 or $30 for a $1. Of course you will never see that price so it is a completely futile excercise. However if you think that horse A looks to be at fair value at his current price of 3-1 and horse b looks to be at fair value at his current price of 6-1 then you could just use the formula, (3*6)+3 or $21 for a dollar as the fair exacta price as a point of reference. Making a line is much more accurate, but of course a lot more time consuming.

[HalvOnHorseracing]

Originally Posted by Poindexter

If you are talking about from your own oddsline, the math is fairly simple. Say you have the 1 horse 2-1 and the 6 horse 8-1

.333333 chance the 1 wins and should he win the 6 has a .111111111/.666666666 chance of beating the rest of the field

so the chances of hitting are 1/3*1/6 or 1/18 which is a fair value of 17-1.
Actually the formula to determine the exacta price needed is much easier than that. Simply put it is :

(win odds*place odds)+win odds. So in the example I gave (2*8)+2=$18 for a $1 exacta. So the good news is you can likely do this in your head.

Now if you are using the public's line you would have to adjust for the takeout, so assuming a 15% takeout if the public had the 1) 2-1 and the 6) 8-1 the 2 becomes .33333/1.15 or .29(around 5-2) and the 8-1 becomes .1111111/1.15 or .096. More like a 9.5-1 shot. EDIT-I think my math is probably wrong on the public line.

Now all this assumes that the place line matches the win line, which is seldom the case in racing.

FWIW, I do not use this model myself even when I do line races.

Like much of your math, the calculation is interesting. The flaw is that once you put a horse in the win slot, the probability of that horse finishing second becomes zero and the probability of a horse from the rest of the field finishing second is 100%. Which is also why the place line can't match the win line. And of course the odds of any horse finishing second do vary based on which horse wins the race. It is almost a given that calculating the exacta odds has to parallel the win odds. I actually agree that you somehow have to make the calculation based on win probability for the sake of simplicity. I'm not criticizing the technique. It's actually better than people betting while not having a clue whether the exacta is underpaying or overpaying.

If you are using the public line - either the morning line or the tote board odds - that line has already the take computed. A good line maker makes a 115-120% line, and of course the tote board odds are after the take has been deducted.

I've made it easy for people by developing a table for determining if the exacta is a fair payoff based on your real odds, on the thinking that if you make people come up with a win line and a separate place line they'll never do it. It also has some margin of error built into it.

http://halveyonhorseracing.com/?p=4319

[punteray]

Thanks for the replies! I forgot to say it was a method using EXCEL.

[AltonKelsey]

"And of course the odds of any horse finishing second do vary based on which horse wins the race."

Interesting. What would be the calculation for that?

Would it be easier to run second if the favorite wins or a longshot?

The answer is not so simple, I suspect.

[AltonKelsey]

Just thought of something, do the odds of the winner vary based on who runs second.......

Just a thought.

[Poindexter]

Originally Posted by AltonKelsey

"And of course the odds of any horse finishing second do vary based on which horse wins the race."

Interesting. What would be the calculation for that?

Would it be easier to run second if the favorite wins or a longshot?

The answer is not so simple, I suspect.

The Math is simple. Say in a race we have

horse 1) 1-1 (50%)
horse 2) 4-1 (20%)
horse 3) 20-1 (5%)

Horse 3 has a 5% chance of winning. No matter who wins, he theoretically would have a 5% chance(of the remaining % left) of beating the rest of the field. So if the favorite wins there is 50% probability left on the remaining horses. So the 3 should have a 5/50 or 10% chance of coming 2nd. So the chance of the 1-3 exacta is .50*.1 or .05 or 20-1. If the 2 wins the 5 has a 5/80 or 1/16 chance of coming 2nd.............................

The problem is this is not accurate because of things that happen in a race or the win or miss nature of some horses. For instance a horse that won for 25 k last week, now drops for 16. You factor in the suspicious drop and make him 8/5 or about a 38% chance of winning. Now amongst that 62% chance you give him of losing is a significant chance that he just went no good. Now it gets even more complex, because sometime even when they are no good, they still manage to run a well beaten 2nd. So it is a very inaccurate math with these types. A lot ot trainers really have a knack for knowing just how bad there horse went. Also, factor in the nature of racing, 2 horses figure to duel on the lead, can they both hang on to run 1-2, sometimes, but often someone will split them or one will stop worse. Then you have layoff horses. There is a siginificant chance that they will be out for excercise or not ready and if they lose, they have nowhere near the same chance of coming 2nd as winning, but many of them do come 2nd. Then you have 1st time starter, 2nd time starters, first time turf, horses stretching out, horses shortening.......Then of course you have horse that refuse to win or distances that give certain styles a much better chance of coming 2nd/3rd than winnin....Then you also have the live horses, horses that you can't see but the money is all over them. So many of these horses very well. It is just a very inaccurate estimation process mainly because of the variables involved in your typical horse race. Which is why I personally focus on the value horse(s) and not worry about the "value exacta".

But if this works for people, great. I found that it was too inaccurate and thus abandoned it.

[AltonKelsey]

I like your answer, but think about the second question. Why is running second any different than winning? Or running last?

If you had to assign place ONLY odds in advance , wouldn't there be one set of odds, irrespective of who finished in the win slot? I think so.

So the odds of a horse running second , is independent of who wins.

Try wrapping your head around it before you say its crazy.

[Poindexter]

Originally Posted by AltonKelsey

I like your answer, but think about the second question. Why is running second any different than winning? Or running last?

If you had to assign place ONLY odds in advance , wouldn't there be one set of odds, irrespective of who finished in the win slot? I think so.

So the odds of a horse running second , is independent of who wins.

Try wrapping your head around it before you say its crazy.

I don't think it is crazy at all. I think you mean odds to run 2nd only and not place. Sure you can do that

So you would have a line that looked like this to win

1) 3-1
2) 4-1
3) 6/5
4) 20-1
5) 20-1

Then you might have a to run 2nd line that looked like this.

1) 5/2
2) 3-1
3) 2-1
4) 12-1
5) 20-1

So basically the Math would look like this. On Say a 1-3 exacta
.25 chance the 1 wins * .33/.714 on the 3 coming 2nd leaves you with or .1155 or fair price of $8.65 for a $1 exacta. As opposed to using the win line only which in the above case you would have a fair price of $6.60. You can easily program a spread sheet to calculate all of the payoffs for you. Or if you want to save time and effort just multiply win odds of the top horse by place odds of the 2nd horse+win odds of the top horse. It will be less accurate(It would come up with $9 instead of $8.65 in the example I just gave) but you do not have to go through the process of creating a spreadsheet.

It is a good idea and certainly will be more accurate. I think a lot of the factors I mentioned prior still make it a tough task, and it makes the handicapping process a lot more larborious as now you have to come up with 2 lines instead of one, but roll with it and see how it works for you.

[HuggingTheRail]

And if the math decision isn't tricky enough, you could also consider running styles - odds of two deep closers finishing 1-2 is less likely...etc

[TheRinger]

Formula for fair exacta payoff.

=BetSize/(WinProb*(PlaceProb/(1-WinProb)))

[Robert Fischer]

lazy right now, after dinner. Not sure how this explanation will come out.

If I wanted a generic method:
1. I'd look at the win odds for the top slot.
2. I'd then reduce the field size by 1 and rank the contenders for the place position in order using my handicapping insight(as opposed to the remaining public odds).
3 Then I'd use my ranking with Trifecta Mike's Odds Rankings probabilities formula.
3. I'd multiply the win odds% x the odds ranking within the remaining field size, and convert that into an $exacta payout, and consider playing that if I felt that I had an edge.


in the picture above, i used a 10 horse field.
I used the 2-1 favorite(entered in B14 and C14) on top.
Then I ranked the remaining horses for their chance of running 2nd. Since I thought the third public choice, is more likely than the second public choice, I'll consider a play.
I use (C1) because is my top-ranked horse(to fill out the exacta) of the remaining 9 horse field.
Their probabilities multiplied in E15.
then converted to odds in E17.
$17 is my crazy estimate for fair price on a straight - exacta.
Maybe I consider $17, or maybe I want a $5 or $10 cushion or whatever....



not what I personally use, but I don't automate my stuff like this

[Robert Fischer]

forgot to add in the wager to the odds part

so it would be $17X2+2 or $36 not $17 for $2 exacta.

also meant D1, rather than C1.

too much thinking