how many bets to be sure?

[chris001]

A specific selection procedure shows a 78% s/r and a level stake ROI of 4.52% after 200 bets. From a statistical p.o.v. how many bets do you need to have some certainty that this is indicative of how it will continue at this level? Anyone know a formula? Thanks

[slapdash]

Re: how many bets to be sure? Of course, you can never be absolutely certain. But also the answer depends on how much the odds vary. The figures you give are consistent with all bets having odds of 1.34. If this were the case, then the chance of getting a ROI of 4.52% by chance, if the long term expectation was really just to break even, would be about: 200 bets: 15.5% 400 bets: 6.6% 600 bets: 3.1% 800 bets: 1.5% 1000 bets: 0.7% 1500 bets: 0.13% 2000 bets: 0.02% If the odds actually varied, then the probabilities would be higher, depending on how much the odds varied.