The answer is to allow some investors to choose a fixed percentage return of .75 percent. For instance, let's say the profit of the site averaged 2 percent for a given week. The investors that choose the fixed percent would get paid .75 percent and the ones who took the rest of the downside risk would get 2 percent plus .25 for paying the fixed percentage.
In weeks the site has a loss the investors that took the fixed percentage of bets would get paid .75 from the investors that didn't. In this way some investors can lower their variance by giving up some profit and other investors can profit from that.
This is a +ev decision for the investors taking more risk because it ups their longterm returns to 1.25 percent.
This has been discussed several times before. I think Will Phase came up with the idea first, possibly in this very thread.
It doesn't work, and here's why:
Anyone getting a guaranteed return isn't contributing to the site. If you invest 1 BTC today and I have to give you more than that back tomorrow then what use is your 1 BTC? I can't use it in the bankroll because I might lose it. I'm better off just telling you I don't want your 1 BTC, because then I don't have the liability of paying you any interest. There's no upside for me to having investors who aren't willing to take a loss.
Look at it this way: suppose I have just 2 investors. One has a fixed return of 0.5% of 1% of the amount wagered. The other gets the rest (he expects to get his own 1% of turnover plus the other 0.5% of turnover that isn't going to the other guy).
Suppose both players "invest" 100 BTC, and on an average week we have 2000 BTC wagered, and keep the expected 1% of it, ie. 20 BTC. Of that 20 BTC profit, the fixed-return guy gets 5%, and the other guy gets 15% of it. That's cool - the fixed return guy gets a good return, and the regular risk-taking guy gets 3 times as much, rewarding him for taking a risk. It looks like a good scheme, if that's as far as you look.
But what if we have a bad week, and after 2000 BTC was wagered, the site ends up 20 BTC *down*? The fixed-return guy still gets his 0.5% of 50% of the 2000 BTC wagered, or 5 BTC, and the risk taker ends up 25 BTC down, since he has to pay for the house loss as well as the fixed-return guy's profit for the week.
Finally, since we considered what happens when the result is 40 BTC worse than expected, what when it's 40 BTC better than expected, and we end up with a profit of 60 BTC from 2000 BTC wagered? The fixed-return guy gets 5 BTC, as he always does when 2000 BTC is wagered. So the risk taker gets the other 55 BTC.
In summary, how is each person's return in bad, neutral, and good weeks?
fixed return: 5, 5, 5
risk taker: -25, 15, 55
And if the fixed return guy just wasn't involved, the risk taker would get the whole amount to himself:
single regular investor: -20, 20, 60
We can see that the presence of the fixed-return guy has done nothing but drain 5 BTC per week from the other guy's profits, positive or negative.
So what use it he? We can't increase the max profit per bet due to the fixed-return guy's investment. Because he's not risking any of his coins, we can't use them to pay out winners. He's simply a parasite on the regular investors.
Also, assuming this is you in the chat:
16:45:49 (416053) I have some people analyzing the site now
16:46:13 (416053) see the average bet is .02 and 500 million bets
16:46:22 (416053) doesn't add up even with the big bettors
16:46:33 (416053) percentage shoudl be at least .60
Your math is wrong. You can't assume all the bets are the same size. Here's an exaggerated example which shows why:
Suppose there were a hundred bets and that 99 of them were for 0 BTC and one was for 100 BTC. The 100 BTC bet won at 49.5% and the site profit is 100%.
The average bet size is 1 BTC.
You run your simulation and find out that there's no way after 100 bets of 1 BTC each that the site profit should be 100%, but it is.
Do you see the problem? Calculating the "average bet" is meaningless. The "average" couple has 2.3 children. There weren't 100 bets of 1 BTC each. There was a single bet of 100 BTC and 99 bets of zero.
Again, this has been gone over in detail in this thread already, mostly when nakowa was playing heavily.