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Old 02-14-2008, 07:16 PM   #3 (permalink)
chemist
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Quote:
Originally Posted by VideoReview View Post
Is there any who can show how to calculate the cumulative probability of something occurring when multiple probabilities are involved?

I am aware of how to calculate the binomial distribution for probabilities that are constant but not when they vary. For example, if a fair coin was flipped 4 times and I was making a guess each time, the probability of me guessing wrong at least:
4 times is 6.25% or 1 in 16 experiments
3 or more times is 31.25% or 5 in 16 experiments
2 or more times is 68.75% or 11 in 16 experiments
1 or more times 93.75% or 15 in 16 experiments
0 or more times is 100% or 16 in 16 experiments

So, here are some relevant probabilities (actually they are real NHL ML numbers) and there outcomes (1=win, 0=lose):

-111 1
-143 1
-125 0
-135 1
-112 1
-109 1
-107 0
-110 0
-111 1
-116 1
-106 0
-120 1
-110 1
-123 0
-124 1
-118 0
-135 0
-109 0
175 0
216 0
184 0
179 1
150 0
265 0
189 0
185 0
144 1
145 0
152 0
188 0
145 0
185 0
175 1
212 1
178 1
167 1
192 0
180 0
153 1
168 0
180 1
307 1
175 1
170 0
200 1
175 1
236 0
157 0
188 0
222 0
270 1
147 1
164 1
172 1
183 1


Assuming a bet to win an equal percentage of bankroll for each of the above events, my results would be:

Win 48.332811 units, Bet 41.766906 units for a net ROI of 15.7%.

2 questions:

1) What was the probability that I would win "at least" the 15.7% that was obtained during this experiment and how is that calculated?
2) How do you calculate the probability of winning or losing various ROI amounts? (e.g. win 2%, 5%, 10%, etc.)

There are bonus smiley faces etc. if Excel type formulas are included with math notations answers.
I know nothing of Excel. In this case a reasonable null hypothesis is that the no-vig ML is the true probability. Computing the probability of M or more successes in N trials of this sort is straightforward but laborious. You could reasonably use the normal approximation and the fact that the variance of the sum of independent events is the sum of the variances of the events. The variance of single binomial trial is p*(1-p).

HTH
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