House-edge information and a volatility warning lead to reduced gambling expenditure: Potential improvements to return-to-player percentages.

Cost-of-play information is one public health intervention recommended to help reduce gambling-related harm. In the UK, this information is given on electronic gambling machines in a format known as the "return-to-player", e.g., "This game has an average percentage payout of 90%." However, previous evidence suggests that this information could be improved by equivalently restating it in terms of the "house-edge", e.g., "This game keeps 10% of all money bet on average." A "volatility warning," stating that this information applies only in the statistical long-run, has also been recommended to help gamblers understand cost-of-play information. However, there is no evidence comparing these information provisions' effect on gamblers' behavior. An experiment tested US gamblers'(N = 2433) incentivized behavior in an online slot machine, where this information was manipulated between-participants along with a counter showing the total amount bet. Preregistered analyses showed that participants gambled significantly less when house-edge information or a volatility warning were shown compared to standard return-to-player information, with no effect of the total amount bet counter, and no significant interaction effects. However, these significant findings had small effect sizes, suggesting that a public health approach to gambling should not rely on informational provisions only. Subject to supportive evidence from more ecologically-valid designs such as field studies, these results suggest that improved cost-of-play information could lead to reduced rates of gambling expenditure and therefore benefit a public health approach to gambling.