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Odds versus probability

27 July 2011

I absolutely love your column and answers to all our questions. It's nice to know there is someone who tells it like it is with no jive one way or the other.

I would like to know your thoughts on possibility (the odds) vs. probability. You tell people, rightfully so, that the odds of hitting a jackpot immediately after hitting one is exactly the same. Being an accountant I know that is true, however my argument is that the probability has changed. If the machine pays a jackpot once every 100,000 spins and it hits the first jackpot on spin 10,000, then the probability becomes that it will only hit one more jackpot in the next 90,000 spins. Therefore on the average I personally change machines shortly after a big win. Of course there is no knowing that the next machine is not in the same "probability mode" as the one you just left.

Your thoughts please?

Ron

Dear Ron,

Thanks for the kind words about my column.

Odds, chances and probability are just different ways of expressing the likelihood of an event. In your example of the jackpot that hits on average once per 100,000 spins, the probability of hitting the jackpot is 0.00001. Many people have difficulty relating to a decimal number. So another, equivalent way to express the likelihood of hitting the jackpot is to say the chances of hitting it are 1 in 100,000. We can also express the likelihood as odds. The odds for hitting the jackpot are 1 to 99,999.

Now, in your example, the machine hits the jackpot on spin 10,000. In the next 90,000 spins, it might hit 0 jackpots, 1, 2, 3 or even more.

We don't know how many jackpots might hit in the next 90,000 spins. But we do know that the odds of hitting a jackpot on any given spin is 1 to 99,999.

Because odds, probability and chances are equivalent ways of saying the same thing, if the odds stay the same, the chances and probability stay the same too. There's no such thing as "probability mode."

The odds, chances and probability of hitting the jackpot are the same on every spin.

Best of luck in and out of the casinos,
John


Send your slot and video poker questions to John Robison, Slot Expert, at slotexpert@comcast.net. Because of the volume of mail I receive, I regret that I can't reply to every question.

John Robison

John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots
John Robison
John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots