"Line-math" weenies check in please...

[fitguy67]

On another thread, it was stated that DAL-7, -110 corresponds to DAL-6.5, -124.1

_________

I obviously don't understand the accepted conversion method...cuz by my reasoning...

DAL-7,-110 would correspond to -6.5, -118.46 (which implies a 7.14% worse payout [say, per-hundred] than the old line...to offset the degree to which the new "-6.5" is better than the old "-7"...meaning a pph of 84.42 versus the old 90.91...meaning 100/84.42, which is 118.46/100=-118.46)...

______________

What i'm doing is clearly NOT CORRECT...so i ask

what is the accepted method (and the basic logic behind it) for this sort of calculation?

DO NOT link me to a web-based "black box" calculator...(but an "xls" file would be great as long as i can read the formulas)...I want to understand the logic behind the accepted method for imputing value-equivalence of lines differing only by the "number" (referring to either "spread" or "total")...usually by just a half-point.

[dice]

On another thread, it was stated that DAL-7, -110 corresponds to DAL-6.5, -124.1

_________

I obviously don't understand the accepted conversion method...cuz by my reasoning...

DAL-7,-110 would correspond to -6.5, -118.46 (which implies a 7.14% worse payout-per-hundred than the old line...to offset the degree to which the new "-6.5" is better than the old "-7"...meaning a pph of 84.42 versus the old 90.91...meaning 100/84.42, which is 118.46/100=-118.46)...

______________

What i'm doing is clearly NOT CORRECT...so i ask

what is the accepted method (and the basic logic behind it) for this sort of calculation?

DO NOT link me to a web-based "black box" calculator...(but an "xls" file would be great as long as i can read the formulas)...I want to understand the logic behind the accepted method for imputing value-equivalence of lines differing only by the "number" (referring to either "spread" or "total")...usually by just a half-point.

I have no idea what this means and why you're bringing math into it. Moneylines don't equate to point spreads.

[gauchojake]

No systems in PT

[flocko76]

don't know the math, but the think tank has a half point calculator under tools. it depends on what the book actually charges to move off of 7, but from what i gather, the -124.1 is based on a -4.55% edge.

[mathdotcom]

On another thread, it was stated that DAL-7, -110 corresponds to DAL-6.5, -124.1

_________

I obviously don't understand the accepted conversion method...cuz by my reasoning...

DAL-7,-110 would correspond to -6.5, -118.46 (which implies a 7.14% worse payout [say, per-hundred] than the old line...to offset the degree to which the new "-6.5" is better than the old "-7"...meaning a pph of 84.42 versus the old 90.91...meaning 100/84.42, which is 118.46/100=-118.46)...

______________

What i'm doing is clearly NOT CORRECT...so i ask

what is the accepted method (and the basic logic behind it) for this sort of calculation?

DO NOT link me to a web-based "black box" calculator...(but an "xls" file would be great as long as i can read the formulas)...I want to understand the logic behind the accepted method for imputing value-equivalence of lines differing only by the "number" (referring to either "spread" or "total")...usually by just a half-point.

1. Calculate the no-vig probability on the spread of 7. If pinn is dealing -7 -110/-110 then that probability is 0.5.
2. Calculate the probability of Dallas winning by exactly 7. Suppose it's 0.05. Then the 'no vig probability' of Dallas -6.5 cashing is 0.55.
3. Convert the no-vig probability of 0.55 into a line. That's about -122 (break even probability of 0.5495).

The key is knowing what the 7 is worth.

[MonkeyF0cker]

On another thread, it was stated that DAL-7, -110 corresponds to DAL-6.5, -124.1

_________

I obviously don't understand the accepted conversion method...cuz by my reasoning...

DAL-7,-110 would correspond to -6.5, -118.46 (which implies a 7.14% worse payout{say, per-hundred** than the old line...to offset the degree to which the new "-6.5" is better than the old "-7"...meaning a pph of 84.42 versus the old 90.91...meaning 100/84.42, which is 118.46/100=-118.46)...

______________

What i'm doing is clearly NOT CORRECT...so i ask

what is the accepted method (and the basic logic behind it) for this sort of calculation?

DO NOT link me to a web-based "black box" calculator...(but an "xls" file would be great as long as i can read the formulas)...I want to understand the logic behind the accepted method for imputing value-equivalence of lines differing only by the "number" (referring to either "spread" or "total")...usually by just a half-point.

This should really be in the Think Tank.

I'm not sure where you're getting your numbers from, but this is related to push frequencies. You need to know what the 7 is worth - how often the spread would land on 7 if the spread is at 7. Once you know that, the calculation is easy. Since you're only moving off of the 7, you'd divide the push rate by half and add it to the fair value of the spread. In other words, if the spread is 7 -110/-110 and the spread would land on 7 5.72% of the time, the fair probability for a spread of 6.5 would be 0.5+(0.0572/2). The line would then be -112.134.

The key is knowing what each number is worth.

[fitguy67]

thanks, mathy and Monkey...i strongly-suspected there were "institutional" elements to this that my simplistic inherent-value approach missed completely...

i guess trusting in a good online calculator is the only way to go, then, for ESTIMATING comparable-value prices for differing numbers-of-points

[MonkeyF0cker]

1. Calculate the no-vig probability on the spread of 7. If pinn is dealing -7 -110/-110 then that probability is 0.5.
2. Calculate the probability of Dallas winning by exactly 7. Suppose it's 0.05. Then the 'no vig probability' of Dallas -6.5 cashing is 0.55.
3. Convert the no-vig probability of 0.55 into a line. That's about -122 (break even probability of 0.5495).

The key is knowing what the 7 is worth.

LOL. Almost identical last sentences.

The push rate should be halved though. Using the entire push rate would be a move from 7.5 to 6.5.

[MonkeyF0cker]

thanks, mathy...i strongly-suspected there were "institutional" elements to the calculation that my simplistic inherent-value approach
missed completely...

i guess trusting in a good online calculator is the only way to go, then, for ESTIMATING comparable-value prices for differing numbers-of-points

That's actually a rotten way to go. Either use Pinnacle dropdowns or preferably your own database.

[fitguy67]

i see the point now...the value of half-/whole-point changes is related to the "actuarial" distribution of how same-lined games have turned out in the past (not on a simple arithmetic comparison of the new and old values, as I had done)...as well as the book's need to maintain a markup on the changed probabilities involved...

I've always used Pinnacle and b365's generous-variety of line-choices (and the percentage changes involved in jumps among them)...

i just got curious if there was a reasonably-straightforward way to do the math that underlaid those choices...now i realize it's not the simple algebraic thing i'd naively assumed

[MonkeyF0cker]

i see the point now...the value of half-/whole-point changes is related to the "actuarial" distribution of how same-lined games have turned out in the past (not on a simple arithmetic comparison of the new and old values, as I had done)...as well as the book's need to maintain a markup on the changed probabilities involved...
i guess these sorts of things are built into the calculator

You mean the half point calculator? Yeah. The calculations are built in, but I very much doubt the push rates have been updated in the last four years - since Ganch (who wrote it) left.

If you're just trying to get an approximation, it's still useful though.

[mathdotcom]

LOL. Almost identical last sentences.

The push rate should be halved though. Using the entire push rate would be a move from 7.5 to 6.5.

Not when you've had 4 beers

MONKEY SHARP AS A TAC

[fitguy67]

Summary (aka. things I learned from Monkey and Mathy)

1. there is no straight-forward algebraic method...books consider the historically-based probabilities of similarly-lined games winning/losing/pushing and adjust the line according to the changed probabilities (and their need to maintain the same vig "markup")...

2. best thing to do when u need to know if an alternate line is ok...is to refer to books with a generous menu of different-numbered lines (Pinnacle with the sharpest lines...Bet365 with the widest selection if you need to consider something further away than Pinnacle makes available) and use the %differences that apply to the number-changes you're interested in...

3. the half-point calculators available here and elsewhere are a guide, but if not periodically-maintained (they very likely are not) to include recent results (that books definitely incorporate into their line-setting protocols)...they grow less and less dependable as such

_______________________

I hereby declare that this thread has fulfilled it's purpose...

[wantitall4moi]

its worth what a book charges nothing more, there is nothing that determines what it is worth for that particular game.

any push rates are based on past performances over all games, therefore they are meaningless to specific games, all they do is give a guideline. This isnt cards or dice or something with a finite chance of happening. its sports where anything can happen.

But 'worth' and 'value' change. The 3 is the most obvious example. I have shown time and time again how much it has fluctuated over the years. Pre 2000 games lined -3 pushed about 11% of the time. From 1994 to present it is roughly 9.1% of the time. BUT even in regards to home and away the difference is staggering.

68 of 738 games lined -3 have landed with the fav winning by 3 since 1994 (to the end of last season). Of those the home team that pushed on 3 was 41 of 421 (9.7%) road team -3 was 27 of 317 (8.5%) pretty big difference in so called probability.

Now looking at games from 1994 to 2000 there were (only) 260 games 27 of them landed on 3 (10.5%). From 2001 to the end of last season there were 476 games lined -3, of those 36 landed on the 3 (7.5%) longer time frame many more games and a lot smaller result(chance). So the 'chances' of the 3 dropped from nearly 11% down to 7.5%.

So what do you do? Do you take the last 11 years or do you take the last 18? Or even more? Generally the larger the sample size the better, but that is based on math. Since football has changed it rules and its scoring and many other things you have to look at the most relevant data and use that, even if the sample size is smaller.

Again this is using past results to determine future 'probability'. Which isnt going to work, because anyone who thought in 2000 that they could pay 25 cents to buy off the 3 and be 'right' would have gotten buried because at 7.5% it isnt 'worth' nearly that much. At 10% it is barely 'worth' it.

As far as the -7 goes, over all since 1994 to 2011 there have been 313 games lined (closed) -7, of those 21 landed on the fav winning by exactly 7 (6.7%). Home teams lined -7 are 13 pushed of 225 games (5.8%) and obviously road -7 teams are 8 pushes of 88 games (9.1%)

So take these numbers for what they are.

But if you want to take it one step further Dallas has been a 7 pt favorite 19 times since 1994, they pushed 1 time. So 1/19 (5.25%); and to go even a step further TB has been a 7 pt dog (only) 14 times since 1994, considering how bad that team was that is a very small number, but that aside, they have one push in those 14 game. So 1/14 (7.1%).

And the final step Dallas and TB faced each other in week 15 last year and Dallas was a 7 pt fav, Dallas won by 16, and it wasnt even that close.

What does all this mean? Absolutely nothing but some guys think it does when they try to figure out what a half a point is 'worth' in a certain situation.

[iifold]

Patriots ML...