An investigation by the Verge has shed light on the business of slot machines in US casinos

Traditional slot machines used to pay out on 3% of spins, but those manufactured today return at a rate of 45%, according to an article by Andrew Thompson in the Verge.

That’s not down to the generosity of manufacturers but can be explained by psychology and goes back to an experiment by BF Skinner, who discovered that a pigeon was more likely to press a lever that gave it a pellet of food on random presses than when every single try gave out the prize.

As Thomson writes: “Too little reward and the animal becomes frustrated and stops trying; too much and it won’t push the lever as often.”

Here are six other winning tidbits from Thompson’s piece about the history and economics of slot machines:

1. The first slot machine came at the turn of the 20th century

The Liberty Bell Machine, invented in 1898, had three reels with 10 symbols and paid out in coins, making it the first true incarnation of the modern slot machine. This combination gave punters a one-in-1,000 chance of hitting the jackpot. It is a far cry from the random number generators of today’s equipment.

2. Slot machines have become dominant in casinos

Despite the classic image of cards, croupiers and chips, table games now take up just 20% of space in the standard modern casino. The rest of the floor is dedicated to slot machines, which account for 70-80% of most outlets’ revenue – an increase from 50% in the 1970s.

This draws a lot of parallels with the spread of fixed-odds betting terminals in the UK. Campaigners say bookmakers have been opening multiple outlets on the same high street to get around the legal limit of four per shop.

3. Slot machines compete for customers with distinct themes and designs

The Wheel of Fortune is enduringly popular, apparently, while other TV- inspired designs mentioned in the piece include Friends and Entourage. There are 2,500 different machines on the floor of the MGM Grand, with hundreds of different themes.

One company, IGT, makes 93% of the world’s video poker machines and is the largest manufacturer of video slots in the world. Video poker has been described as the “crack cocaine of gambling”. In explaining the key principle behind the machines, IGT’s founder, William “Si” Redd, said: “If you were to take $100 and play slots, you’d get about an hour of play, but video poker was designed to give you two hours of play for that same $100”.

In other words, the time in which a player’s money is consumed is lengthened. There are no one-off big wins or big losses; instead the game is a flow, volatility is low and the sense of risk is drip-fed.

4. Curved screens help grab attention

A curved screen on a slot machine can increase gameplay by somewhere between 30% and 80%. The only reason: “It looks cool; it’s incredibly clear.”

5. Everything is data-driven

The bank of customer data at Caesar’s Entertainment is estimated to be worth approximately $1bn, according to a recent appraisal by creditors, making it the company’s most valuable asset. Player tracking helps companies understand what keeps people hooked on their machines, and even to calculate the amount gamblers would be willing to risk financially.

6. Small-but-long-term gamblers can be as profitable as high rollers

Over a lifetime of spending, regular customers who keep coming back to slot machines to gamble a little each week can be worth as much as those who go big on Vegas tables.