Ask the Slot Expert: What influences how frequently a bonus round can hit?

Has this ever happened to you?

You're playing one of your favorite machines. A stranger (or a friend) sits down and starts playing the identical machine next to you. You haven't hit a bonus round since the last time Halley's comet was in the neighborhood, but the person playing next to you is not only getting their fair share of bonus rounds, they're getting your share too.

Has this ever happened to you? (Of course, it has.)

The reason your neighbor is getting more bonus rounds than you are is due to the random selection of outcomes on a slot machine. That's just the luck of the draw. There's nothing you, your neighbor, or the slot nerds who worked out the math of the game can do about that.

The slot designers can, however, affect the probability of hitting the bonus round. Let's look at the factors that influence the probability of hitting a bonus.

First, the origin story for this column. I'm a sucker for Egyptian-themed slot machines. Two machines I've played recently are Scarab and Magic of the Nile. Both of these machines have a free games bonus triggered by landing three or more bonus symbols on the screen.

A few days ago, I decided to try a new-ish machine that has been calling out to me, Angel Blade Kingdom of Ice. This machine also has a bonus round triggered by a scatter pay.

My estimate for how frequently a bonus round hits is about 1 in 100. Sometimes I've gone hundreds of spins without hitting a bonus and sometimes I've gotten multiple bonus rounds before playing 100 spins. Overall, I think I'm averaging about one bonus round per 100 spins on most machines.

But not on the three machines above. I have hit the bonus rounds less frequently in my experiences playing them.

Assuming that it is not just my bad luck, what else could be causing these bonuses to hit less frequently?

In slot-industry jargon, any event that can pay the player other than the base reel-spinning game is called a feature. You may have even seen your machine display a message like "Feature pays $xxx" after you've hit some sort of bonus.

For the purposes of this column, I'm going to make a distinction. Bonus round will refer to an event triggered by landing a certain number of triggering symbols on the screen, a scatter pay. Feature will refer to everything else. The need for this distinction will be apparent in a moment.

The main factor that influences how frequently a bonus round can hit is how much it is worth. When slot games with bonus rounds became widespread about 20 years ago, slot designers in a seminar I attended described the dilemma they face. Players want to get to the bonus round frequently. Players also want to win a lot in the bonus round. The dilemma, the designers said, is that players can't have both.

If a bonus round is going to hit frequently, it can't pay very much. But the bonus round also has to pay enough so players don't feel cheated when they finally hit it, like I did today when one of my bonus rounds paid $7.

The balancing act that the slot designers have to play is to make the bonus round hit frequently enough that players have a reasonable chance of hitting it and that it pays enough that players feel it is worthwhile to continue to play in hopes of hitting the bonus round.

In addition to how much a bonus round pays (on the average, of course), other features on the machine affect how frequently a bonus round hits.

Both Scarab and Kingdom of Ice have a feature that occurs on every tenth spin. On Scarab, any position in which a scarab symbol landed on the prior nine spins will be wild on the tenth. On Kingdom of Ice, a fairly complicated tenth-spin feature puts wild symbols or wild reels or a multiplier (or a combination of the three) on the spin.

These regularly occurring features decrease the probability of hitting the bonus round.

Magic of the Nile has three obelisks above the game screen. The colors of the obelisks are green, red and blue. Each obelisk corresponds to a specific feature: Random Wilds, Expanding Reels, Multiplier Wilds. Each obelisk is divided into three segments. When a gem lands on the screen, it lights up another segment in the correspondingly colored obelisk. A feature is triggered when all three segments are lit.

Although we can't count on one of these features being triggered on every tenth spin, they are triggered relatively frequently -- certainly much more frequently than the free games bonus round is triggered. It's not unusual for me to hit multiple obelisk features in a session and not one bonus round. The obelisk features mean that the bonus round won't hit as frequently as my estimate.

Everyone wants to hit high-paying bonus rounds frequently. When a game has additional features, its bonus round is probably going to hit less frequently than on a machine that has no additional features.

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