A study commissioned by the gambling equipment industry's largest trade association found slot machine hold percentages have increased a combined 14.5 per cent across the US over the last 10 years while the revenue from the games has grown just 1.1 per cent.

Slot hold - the percentage of wagers held by the casino - could be associated with the amount of money gamblers bet on the games, or lack of it.

“If players have a bad experience, they might not come back,” said Marcus Prater, executive director of the Association of Gaming Equipment Manufacturers, which hired Las Vegas-based advisory firm Applied Analysis to compile the statistics.

According to the study, tighter slot machines have not meant increased gaming revenue. Actually, the hold percentages could be a reason for the declines.

Prater said casino operators and slot machines makers have heard complaints over the years from loyal customers that the games have grown “too tight.”                                                                                                                                                                                       

Those concerns gave the trade group the idea to investigate. “It's a topic that we've chatted about informally for literally 15 years,” Prater said.