Originally Posted by
wantitall4moi
your bets only resize due to % of your shrinking bankroll not in terms of win probability. Lessmoney equals less bet size. Which is simple math you dont need a formula to tellyou that.
Your probability in a coin flip never changes, it is a constant, just like the amount of the pay off. All numbers in the coin flip scenario are constant, yet still using full kelly it is possible to go broke, or at least lose enough so you cant bet.
All partial kelly or whatever bastardized forms of the equation does it limit risk size, which any monkey can do. But kelly supposedly has an optimal bet size, which the formula clearly spells out.
Basically when guys find success betting kelly it is because of other factors, so they do well in spite of it not because of it. Which generally means they are winning more than they are losing. But also not betting enough overall to have a risk of ruin. Which I stated. For the most part anything over 2% bankroll percentage on any one play is the absolute max, a one side play anyway (where one side wins you collect the other side wins you lose). You really dont need kelly to figure that out.
All kelly does in terms of theory is give people an amount that is corollary their expected advantage. Which again you dont really need kelly for. Because the percentages kelly will give out are just as flawed as some number you could pull out of your ass.
As for your 'wat' comment. yeah should be 37.5.
But it actually shows the odds you get are something to be mindful of as well, especially in sports betting. odds that are 'too good' will actually cause you to over bet more than 'truer' odds would.
What people always fail to realize with math and sports is if you are using past results to determine a future outcome youre already screwed. And that those results dont equal probability or chance or odds or whatever you want to call it.
The best example, the -3 in the NFL, for years people claimed it had a 12 or 13% chance to come in, which according to some databases of closing lines it did. That is assuming all people agreed what games were lined -3 in the first place. But as time went on the 'odds' dropped because fewer games lined 3 were landing on 3, so eventually it got all the way down to 10%, that was around 2007 (going back to 1994). Now it is somewhere around 9% (1994-2010) at least on the most generic of database searches, thats a huge drop over the past 10 years or so, So pre 2001 it was 12%, and since 2001 (2001-2010) it is around 8%. Does the chance of a coin flip ever change? Do any odds change, especially that much over a short time period? Or is it like the US dollar worth less now than it used to be?
Now I could actually go as far as to say with line shopping and betting early or late one could reduce that 8% to something close to 6% since 2001. Sometimes for a little more vig, but not enough to overcome that big a change, certainly less than buying off the 3 after the fact. So basically guys who used to bet pre 2001 used to determine the price of moving a line of the 3 at around 25-30 cents, actually guys still argue it is worth that much because that is what most books still charge. Which they used 'math' to back up. So at a 6% push rate what does that make buying off worth now?
That is where math fails in sports.
Again way off topic but it also goes to the heart of the underlying thought process of sports bettors.
Its ok to use it to some degree but you cant marry yourself to it.
While it is nice to have databases with subsets and results, and I have databases with openers, closers,and all the moves in between in all the major sports going back almost 10 years, it still doesnt help predict the future. But it gives insight into how games moved, how many times they move, when they moved back and forth, and all the nuances lines and odds take. And ultimately what it shows is that there isnt enough data to gain an advantage. Because line moves are 'right' as much as they are 'wrong'. And in some subsets line moves are wrong versus the opening line, despite the fairy tale that beating a closer is a sure fire way to win. Only way that is the case is if you bet the extremes both ways and hit enough middles. I have run that data as well, and there arent enough winners there either. At least not enough to make it profitable, it does reduce risk a lot obviously, but isnt a money maker.
Sorry to completely derail this thread, but I think the answer to the original question has been answered in quite a few ways.