Variance

[walker77]

I started a betting approach 6 months ago and over 2700 plays made around 130 units, about 5% ROI. Thought this looked pretty solid so stepped it up.

With a bankroll of 200 units, started the year with a strategy of betting between 0.5%-3% of roll depending on the size of the overlay and limits. After the first 400 plays, dropped 60 units, -12% ROI. I know I should know this but can someone calculate the % chance of losing 12% after 400 plays with a 5% edge?

I know it's too early to get scared given the previous performance, but would like to know the odds of downswinging like this. Things are always changing in this game so it's good to be vigilant and able to identify when what you were doing previously may no longer be +ev, without thousands of samples to confirm.

[rjp]

To calculate the odds you need to know the probability of winning. To make this easier, are you speaking of typical 11 to win 10 odds with a ~55% chance of winning? If not then you'll need to be more specific.

As you can imagine you're more likely to go down with say a ~25% chance of winning than you are with a ~75% chance of winning (even though both have a 5% expected return over the long term).

[walker77]

The odds are mostly moneyline and vary greatly, so lets just assume we have 400 bets @ +110 when the true odds (juice free) are +100. So the odds of winning each bet are 50%.

Another way, what's the chance of a BM losing 12% after 400 bets @ -110 from a player expected to hit 50/50?

Thanks.