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The maximum rewards at the minimum price: Reinforcement rates and payback percentages in multi-line slot machines

Kevin Harrigan, Michael Dixon, Vance MacLaren, Karen Collins, Jonathan Fugelsang


Past research has shown that gamblers frequently use the mini-max strategy in multi-line slot machines, whereby the player places the minimum bet on the maximum number of lines. Through a detailed analysis and explanation of the design of multi-line slot machine games, we show that when using the mini-max strategy, the payback percentage remains unchanged, yet the reinforcement rate is significantly increased. This increase in reinforcement rate is mainly due to spins in which the amount won is less than the amount wagered, which we call losses disguised as wins. We have verified these conclusions by playing an actual slot machine game for 10,000 spins and recording the results. We believe that the high reinforcement rate that results from playing multiple lines on games of this type contributes to their potential addictiveness. We provide three theories for why players use the mini-max strategy and suggest further areas of research.


slot machines; electronic gaming machines; EGMs; gambling; payback percentage; operant conditioning

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