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Best of John Robison

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Ask the Slot Expert: Slot machine hit frequency, payback and volatility

20 November 2013

Recent articles remind me of getting an answer from Casino Player magazine about whether to stay or stray from the machine. The answer was because of volatility I should stay.

That's what I think is "wrong" with slots. High volatility and LOW hit frequency. Both make the player's bankroll very volatile. RNG and all that is great but... Volatility is programmed into the slot and that's why casinos want to know the volatility index of the machine from the manufacturer so they can see how much they can get from that machine. The rest is up to us to read your articles and those in Strictly Slots continuously telling us to stretch our bankrolls by playing less coins and making a plan before we play.

Also recently we went to Borgata. I noticed that new slots such as Hot Shot Progressive, which is 20 lines as advertised, Borgata made them 9 line. Why? Sure it's great for bankroll but I don't get it. Of all the new games I played only 2 were 20 line (Monopoly) or 10 plus 4th reel and 4+5 for the Extreme reels slot. All the rest were 9 line.

Even if they play the same what about the manufacturer specs in Strictly Slots that usually give 40 percent or more for hit frequency for a 20 line game. What does 9 line do?

Let's go over volatility, hit frequency and long-term payback, what they are and what determines them. The symbols on a machine are distributed on the stops on its reels. Each stop on each reel can join with each stop on every other reel to make a combination. Some of those combinations are winners, some are losers. The ratio of the number of winning combinations divided by the total number of possible combinations give us the machine's hit frequency. The hit frequency is determined by the layout of the symbols on the reels and nothing else.

The paytable tells us how much each winning combination pays. When we weight each winning combination with how much it is worth and divide by the total number of combinations times the number of coins played, we get the machine's long-term payback. The long-term payback tells the percentage of the money played through the machine that will be returned to its players. If we take the long-term payback and subtract it from 100 percent, we get the house edge -- the percentage of the money played through the machine that the house will keep. The long-term payback (and thus the house edge) are determined by the layout of the symbols on the reels and the paytable and nothing else.

The volatility index also arises from the layout of the symbols and the paytable. It is based on the standard deviation of the paytable and it is used to calculate the range in which we expect a machine's payback to fall after a certain number of spins. The higher the index, the larger the range. The center of the range is the machine's long-term payback. Part of the range can be above 100 percent. The range narrows the more play a machine gets. Casinos want to know the volatility index so they estimate how many spins it will take for the range to fall completely below 100 percent.

Casinos can lose money on machines. If you've ever been in a casino shortly after it opened, you've seen players hit jackpots that exceed the total amount of money that could possibly have been played on a machine. The casino is -- temporarily -- showing a loss on those machines. Casinos can't control when their machines hit winning combinations, so they have to be patient for a machine to show a profit.

I once attended a seminar given by someone who was involved with the development of the Blazing 7s slot machine. He said the machines were doing very well in one casino, so another casino decided to install them. The second casino was not as lucky -- because it's players were. The second casino showed a loss on the machines for longer than they were used to because the machines were so volatile and its players so lucky. As the machines in the second casino got more and more play, their actual paybacks got closer and closer to their long-term paybacks and the casino started to make money from the machines.

Now, addressing your letter, volatility isn't really programmed into the machine. It's a consequence of reel layout and paytable. We can change either one or both to change a machine's volatility. Some people like low hit frequency machines and the wide bankroll swings they provide; some don't. If you choose to play a low hit frequency machine, you will probably need a larger bankroll to see you through cold streaks than if you had played a higher hit frequency machine.

Many games are available in multiple configurations, 9 lines versus 20 lines, for instance. Maybe Borgata thought they had enough 20 line games or it doesn't think its clientele like games with so many lines. In any case, we'd have to see the PAR sheets for the games to know their hit frequency. It could be higher than, lower than, or the same as that of the 20-line version.

Finally, I think you should stay with a machine as long as you're having fun playing it. What has happened in the past tells us nothing about what will happen in the future. We can't predict what the future will bring, so stay with a machine if you're still having fun and find another if you're not.


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