With both sides of the coin being equal heads 50% Tails 50% equaling a total probability of 100%. My question is would it make any difference if instead of using 100% as total if we used 90%? so heads would be 45% and tails 45%.

The reason i ask is from a bookmaking and professional bettors point of view.

A true market is 100% but bookmakers usually would set their market to 110% (10% being the juice) but ideally you would look to assess your market from the bettors point of view to around 80%-90% to turn the margin into your favour, as opposed to the bookmaker who bets overound to 110% or therabouts.

So my question is, is there any error in setting the total market to 90% instead of 100?

How is this different from your last question?

I deleted password and didn't save so registered account again. The previous question was asked in this probability forum and mods moved it to the sports betting forum but the question is a probability question not a sports betting question so dont understand why it was moved to the other forum. Ofc the replies in that forum were trolls.

Do you understand the question? if so, interested in your or anybodies answer to the question. For those that don't understand the question ask what you don't understand and i can explain further, but to me its a basic question.

To solve this you don't change the percentages, you change the EV formula.

Let's say you're flipping a coin against someone. If it's heads you gain $1 otherwise you lose $1
EV = 0.5*1 + 0.5*-1 = 0

If instead you lose $1.1 when you lose, because the guy takes juice, then
EV = 0.5*1 + 0.5*-1.1 = -0.05

If it's not a fair flip and instead you have X chance to win, and therefore (1-X) chance to lose, then
EV = X*1 + (1-X)*-1.1
EV = X - 1.1 + 1.1X
EV = 2.1X - 1.1

Rusty has covered it, so I will just add the following.

For any betting situation, it is important to know (and keep separate) the probabilities of the possible outcomes (which must add to one) and the payouts for each possible outcome (could be positive, negative, or zero).

OP is confusing the two. Or at least he appears to be confused.

Thanks for answering. But I don't understand the X*1 + (1-X)*-1.1 and what all this means unless its said in words.

Basically i do understand simple probabilities, but why i am asking this question is from a horse racing point of view. Most horse bettors frame betting markets to 100% so each horse takes a % of probability from that 100% to win the race, so all horses combined equal a 100% in total.

But some bettors prefer to frame their markets to 90% to turn the margin into their favour, as opposed to the bookmaker who bets overound to 110% so its in their favour.

They do this so whatever price they have assigned the horse say $2 decimal in the 90% market its easier for them to see value instantly instead of framing the market to 100% and then say adding 10% to that price $2 and needing $2.20 to back the horse.

So my question is is there some kind of probability error in framing to 90% vs 100%? If there isn't any error is framing the market to 90% then someone can actually frame a market to 10%.

And the horse whos wining probability in a 100% market is 10% would be 1% in a 10% total market value.

Another example is with flipping a coin again since heads and tails are each 50% totaling 100%, but what if instead we used heads 1% heads and tails 1% totaling 2% total.

Does it make a difference if you frame a betting market to 100% 90% or 10% as in is there any probability error in maths etc?

Nothing you said above means anything to me, because it's all sports betting stuff. That's probably why your post got moved. I don't know what "framing a market" is", I only vaguely know what overround is.

You either need to ask this in the sports betting forum, or figure out a way to express what you're asking without resorting to betting terminology. Or I guess wait and hope you get lucky.

The question isn't about picking winners or overlays or sports betting or horse racing its about probability.

another example

why are coin flips 50% each of two totaling 100% why aren't they 1% each of two as i said in previous post. Why is 100% used instead of 2%.

from wiki it explains framing a market https://en.wikipedia.org/wiki/Prediction_market

See where it says 0 or 100%

this is my question, why is 100% used would it make a difference if it was 0 to 90% instead of 0 to 100%? would the probabilities be as accurate with 0 to 90% vs 0 to 100%?

Because when discussing probabilities, when you add up all the options, they add up to 1. It's more or less just a definition in the field.

What you are asking is essentially nonsensical. It's like asking "how come half of a cup plus another half of a cup is a whole cup? Why don't we use 45% of a cup and 45% of a cup?"

You either have some kind of misunderstanding, or you're asking the wrong question.

Maybe, just maybe, this is what OP is talking about.

For simplicity, suppose that there is You and Me (the bookmaker). There is an upcoming horse race between A, B, C, and D.

You subjectively believe that the "true" probs of A, B, C, and D winning are 33%, 34.5%, 20%, and 12.5% respectively.

I subjectively believe that the "true" probs of A, B, C, and D winning are 25%, 40%, 15%, and 20% respectively.

Under my beliefs, the "fair" payout odds would be 3:1, 1.5:1, 5.7:1, and 4:1 respectively.

Under your beliefs, you would have personal subjective +EV if you accepted odds greater than 2:1, 1.9:1, 4:1, and 7:1 respectively.

Okay, suppose I (the bookmaker) need to make money, so I tweak the odds so that I make a 10% expected profit. I do this by "lowering" all the odds by 10%. So the odds I offer are 2.7:1, 1.35:1, 5:1, and 3.6:1 respectively.

This can be thought of, loosely speaking, as "using a 110% probability" baseline. Since it is essentially equivalent to saying that the odds will be tweaked so that the offered odds when converted to probabilities come out somewhere near 110%. (Of course, the offered odds can be derived exactly using 110% of the baseline instead of simply giving each a 10% haircut.)

You, on the other hand, may want to strive for a 10% expected profit. So you do the exact same thing except in the opposite direction. So you will only accept bets that give you >=10% above your "+EV" odds thresholds shown above. Multiplying each of your odds above by 1.1 gives new acceptable odds of 2.2:1, 2.1:1, 4.4:1, and 7.7:1 respectively. (Like for the bookmaker, this can be thought of as taking a 90% probability baseline since the probabilities from your new acceptable odds sum to around 90% -- of course, that is an alternative way to derive your acceptable odds too.)

So I (the bookmaker) is offering:

A: 2.7:1
B: 1.35:1
C: 5.1:1
D: 3.6:1

and you are seeking:

A: 2.2:1
B: 2.1:1
C: 4.4:1
D: 7.7:1

So you would place bets on A and C.

Bottom line: I think OP is using a differential probability baseline as being a short-cut to allowing for a margin, for both the bookmaker and the individual bettor. The greater the distance is from 100%, the greater the margin.

OK and just to explain its not me actually who is saying to use 0 to 90% instead of 0 to 100%. I'm actually saying it should be 100% but many and i mean many professional bettors that frame their own market or as wiki calls it "Prediction market" will say they frame markets to 90% or even 80%.

I say to them i don't understand why you do it to 80% or 90% when its correct to use 100%. But they disagree even articles in horse racing agree with them to frame markets to 90% or 80%.

This is one article for example who teach bettors how to frame a market this is what they say.



http://www.horseracinginfo.com.au/be...own-market.htm



So this is why i asked the question in this forum because as i said horse racing websites that teach bettors, constantly give this same advice to frame to 0-90% so the 10% difference is in the favor, but i didn't think it was the correct way of doing so hence why i asked in this forum. Btw when i tell them i think it should be 100% they will reply it doesn't make a difference if its 90 or 100 as every horse still totals 90% etc

So are you are saying they are definitely wrong to frame to 90%?

Its amazing because as i said its not only that website that says to do to 90% but i would say most of the horse racing websites say to use 90% it seems very standard to them.

Yes baseline seems the word, this is correct the bookmaker would add 10% so it in his favor = 110% total while the bettors does the opposite and frames the market to 90%.

This is my question does it make a difference if its 90% 100% or 110% is there any error probability or maths error if its not done to 100%?

And when i say any error i'm not talking about opinion where the bettor or bookmaker are predicting a market but probability or a maths error?

Can you define "frame the market"? It seems to be a term of art I am unfamiliar with.

i guess he means "bookmaking", or just assigning probabilities of each horse to win.

and for me it would make the most sense to calculate your probabilities to 100% (like it should be), then convert each probability into decimal odds (1/probability) and if bookies odds are higher than yours, you have a valuebet.

Framing betting market explained.

https://en.wikipedia.org/wiki/Prediction_market

http://www.horseracinginfo.com.au/be...own-market.htm


Yeah it would make most sense to calculate to 100% but betting professionals are saying 90% is the same as 100% while others are saying its not the same hence the thread question.

Looking around it looks to me that "framing" the market is just making sure you are assigning odds to each horse that add up to 100% - someone needs to win, right? Framing at 90% is just discounting your odds a bit to give you a little bit more of a separation when compared to the books odds. whosnext explained how it works in detail.

I don't understand that what i am asking ITT is still misinterpreted.

The thread question has nothing to do with how a book works, sports betting horse racing or any betting at all.

The question is if you use 0 to 90 instead of 0 to 100 is it as accurate?

As in is there some kind of probability flaw in using 0 to 90 instead of 0 to 100, again the thread has nothing to do if a horse is Even money or 2-1 etc or if the bookies like it or the bettor like it or if its value or not value etc etc etc etc.

The question, without context, makes no sense.

There's some smart guys here surely they can understand what my question is?

I'm throwing everything at you guys besides the answer to my own question.

OP, you are asking a question that makes little or no sense. Generous folks have attempted to provide some information that may be useful and have even recharacterized your question so that it does make sense (see post 10 for example).

Yet you persist in asking the same question over and over. You have not acknowledged the efforts of the other posters, not a hint of thanks. Your petulance is becoming tiresome and unwanted.

You seem to be unfamiliar with basic probability and expected-value concepts. You seem to be vaguely aware of some betting concepts but do not understand their basic tenets.

It seems like this forum is not being helpful to you. I would suggest talking this through with someone in person since these written exchanges are frustrating and unproductive for all.

I am going to lock this thread at this point.