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Best of John Robison

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More on estimating a machine's long-term payback

19 June 2010

John,

I'm a long time reader and look forward to your insight. In a recent column, you stated:

"A while ago I wrote that you can estimate a machine's long-term payback by estimating how likely each symbol on each reel is to land on the payline. I've done this by noting the outcome of a few hundred spins."

How can the results of a short term session (a few hundred spins) give you enough information to adequately estimate the long term payback (millions upon millions of spins)? If this snapshot analysis happens to be very positive (and it certainly could be) giving you the "statistics" that show a 98% return, isn't this contrary to the reality of how slots actually work?

Thank you,
Joe

Dear Joe,

Thanks for the kind words about my column.

I was a bit too brief in describing what I had done. I kept track of the symbols that landed on the payline and then used that information to estimate how likely each symbol was to land on the payline on each reel. Using those estimates, I estimated how likely each winning combination was.

I didn't keep track of the whole combination -- that would require tens of thousands or more spins to get a good estimate -- rather, I tracked the individual symbols.

Let's say there's one jackpot symbol on each 32-stop virtual reel on a machine. In the course of, say, 100,000 spins, you might never hit the jackpot, leading you to believe the combination was impossible to hit or nearly so. But looking at the individual reels, you see that the jackpot symbol landed on each reel about 3,000 times -- just not all at once -- leading your estimate of the jackpot symbol's landing on the payline close to 1/32 for each reel and your estimate of hitting the jackpot close to the actual probability of 1/32,768.

Because I was tracking and estimating each symbol on each reel, and not the combination of all reels, I needed far fewer spins to build my estimates.

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