Gotta Catch 'Em All

Gotta Catch 'Em All

How random number generators make video games addictive.

by Andrew Fishman, MSW, LSW, Clinician, Response Center for Teens

(This blog, part of a series, originally appeared in Psychology Today under the title Gotta Catch 'Em All.

Response Clinician Andrew Fishman sometimes sees young people whose video game use can be problematic. While there are many reasons that people of any age may overuse gaming, in this article, Andrew explains how the use of “random number generators” make video games more exciting, and potentially addictive, similar to the way casinos operate.

How random number generators make video games addictive

In December 2016, a man playing Pokémon GO while driving a construction crane hit and killed a woman who was riding a minibike.  Ten days later, a middle school teacher playing Pokémon GO veered off the road and struck two pedestrians.  Dozens of similar cases have been reported since the game was released in 2016.  

This is tragic, but not at all surprising, based on how the game is set up.  

The idea of video game addiction is becoming more mainstream.  The World Health Organization recently added it to their list of recognized diseases and the DSM 5, the guide mental health professionals use to help diagnose clients, added it as a “condition for further study.”  However, critics point out that it’s difficult or impossible to distinguish from depression.  

This was cleverly summarized by an author who wrote, “we would not diagnose depressed individuals with hypersomnia with a comorbid ‘bed addiction.’”  In other words, a person with depression is likely to spend a lot of time in bed, but that does not mean that he is “addicted” to his bed.  

In the same way, someone playing too many video games becomes a chicken-and-egg problem; are they spending all their time in their room playing video games because they’re addicted to the games, or are they playing so many games because they have depression?  


B.F. Skinner, whose work is often used to make games more engaging, is most famous for his work with operant conditioning.  Simply put, operant conditioning is the idea that people and animals do actions more frequently when rewarded and less frequently when punished.  

Skinner initially developed this hypothesis while working with pigeons, discovering that giving a pigeon a reward every time it did something (like pressing a button) made the pigeon much more likely to do it again.  However, when the reward was taken away, the pigeons quickly stopped trying. This is called a “fixed-ratio” schedule of reinforcement because the ratio of button-presses to rewards is constant. When the reward is removed, the behavior doesn’t usually continue, because the pigeons notice quickly that the button no longer provides a reward. 

However, Skinner noticed that when this ratio is not fixed, the behavior can continue for a long time, even when the reward is removed entirely.  For example, on a “variable ratio” schedule, a pigeon might be given a food pellet after pressing the button once, but it also might take ten or twenty presses before the next pellet appeared.  There was no way for the pigeons to know how many times would be required to earn another pellet, so they continued to press the button over and over, even after the food machine was shut off.  

This is why sometimes giving a dog a treat for sitting on command will make it more likely to retain the skill than always giving the dog a treat. 

For nearly twenty years, video game designers have used this insight to use randomness to make the games harder to put down.  

In 2001, a “game researcher” at Microsoft, who now works as the senior user-research manager at Blizzard (the company behind popular games like World of Warcraft and Overwatch) wrote a guide to help game designers make their games more engaging.  In the article, he explains how to carefully craft game systems to engage players:

"There are also 'variable ratio' schedules, in which a specific number of actions are required, but that number changes every time. A player might be required to shoot down approximately 20 enemy fighters to gain an extra ship, but the precise number is randomly generated each time. It's important to note that the player does not know how many actions are required this time, just the average number from previous experience.

Under variable ratio schedules, participants typically respond with a steady flow of activity at a reasonably high rate. While not quite as high a rate as the burst under a fixed ratio schedule, it is more consistent and lacks the pausing that can cause trouble. Since it's possible (though unlikely) that the player can gain a life for shooting down only one enemy, there's always a reason to go hunting.

In general, variable ratio schedules produce the highest overall rates of activity of all the schedules that I'll discuss here. This doesn't necessarily mean they're the best, but if what you're looking for is a high and constant rate of play, you want a variable ratio contingency."

What is Pokémon GO?

Pokémon GO is an “augmented reality” game, which means that the game adds to reality, rather than replacing it.  While most games create a new world to explore, augmented reality games take reality and makes it more interesting.  

Pokémon, short for "Pocket Monsters," are digital creatures which players can collect, train, and use to battle other Pokémon.  People who play Pokémon GO need to explore the real world to find them.  

As the player navigates around the real world, their character moves along with them so they can find Pokémon in different areas.  Their character only walks when they do.  

Pokémon GO can have a dramatic and positive effect on its players.  Because the game requires players to move, it helps motivate people to leave their homes and walk around.  In fact, thousands of players have raved that the game helped them lose weight or leave the house during a depressive episode.  Several studies have concluded that people who played Pokémon GO exercised more and experienced less psychological distress

The goal of the game is to capture every type of Pokémon by tossing a container called a Poké Ball at it, hence the game’s slogan, “Gotta Catch ‘Em All.”  There are over five hundred different Pokémon available to find in Pokémon GO, with more added every few months.  

Each appears randomly in actual locations for only 30 minutes before disappearing.  The Pokémon which appear are the same for every player; if two people open the game near one another, they will each see the same Pokémon on their screens.  Importantly, the game is “persistent,” referring to the fact that the game continues to exist even when players close the app.  

When players look at the game, they are likely to find “common” Pokémon.  Rarer Pokémon spawn less frequently and some hardly ever appear. The rarer ones tend to be more powerful and are considered highly desirable.  Here’s where the game can become a problem: unless players’ games are open when a rare Pokémon appears, they will miss their chance to capture it.  

This is compounded by the fact that most Pokémon also have a “shiny” version; an extremely rare version which is a different color and has a sparkling animation.  The odds of a given Pokémon being shiny are usually about 1:450. They are neither more powerful nor more useful, however, their rarity makes them a source of great pride for many players.   Players often show off their shiny Pokémon when meeting one another in real life.  

Additionally, not all of the same “species” of Pokémon is equal.  Each Pokémon comes with a set of three unique statistics, or “Individual Values” (IVs).  These represent its health and its ability to attack and defend. One Pikachu might be much more powerful than another.  The odds of encountering a “perfect” Pokémon vary from 1:216 to 1:4,096.  

Because one of the game’s core features requires players to work together using their strongest Pokémon, players whose Pokémon are weaker than their friends’ can feel like they’re letting down their teammates.  In joint combat, these statistics make a difference. A Pokémon with a high attack statistic does much more damage than one with a low number.  

My neighborhood has a Facebook group with 1,200 members who meet up in real life to play the game together. Every day, players post when they see something unique or when they need help fighting something particularly tough. It’s a natural way to meet neighbors with similar interests. I’ve witnessed a number of shy, introverted people leave their comfort zones to interact with other Pokémon GO players.    

Why is it addictive?

There’s an early episode of The Simpsons in which Marge decides to save money by not buying a lottery ticket that week. When the numbers she would have played are called, she is devastated to realize that she could have been rich if she hadn’t stopped gambling. The same fear is often expressed by people who play slot machines; the next quarter they put into the machine might result in a jackpot, which makes it difficult to stop. 

In the same way, each time people who play Pokémon GO have to grapple with the knowledge that whenever the game is off, they might be missing a once-in-a-lifetime chance to get something extraordinary.  

The creators of Pokémon GO seem to have taken the advice of the game researcher to an unusually high degree.  Nearly every action players take includes some element of chance.  Randomness is built into every aspect of the game.  

One Reddit user quipped that “This game is nothing but [randomness].  It’s a random number generator that looks like Pokémon.”  

Each of the following features and aspects is completely determined by the roll of a virtual die.  (This list will not make sense to non-players):

  • Which Pokémon appear in a location
  • Whether a Pokémon will break out of a Poké Ball
  • How often Pokémon block Poké Balls  
  • Whether a Pokémon flees after breaking out
  • Whether a Pokémon will be shiny
  • What Pokémon appear in raids
  • What IVs Pokémon have
  • What IVs traded Pokémon acquire
  • What level a wild Pokémon is
  • How often Pokémon attack when battling in a raid
  • What moves wild Pokémon know
  • What moves raid Pokémon use
  • Which Pokémon nests contain 
  • Whether a friendship will become lucky
  • What items are received by opening a gift
  • Whether a common Pokémon will turn out to be Ditto
  • What items are received from completing a raid
  • Which Pokémon team leaders use
  • When team leaders’ Pokémon use charged attacks
  • What items are received from completing a battle against a team leader
  • Which items are received from completing a battle against a friend
  • Whether Smeargle will photobomb a snapshot
  • Whether a gift will be acquired from a stop
  • What bonus items will be received from completing breakthrough research
  • What bonus items are received from completing a seven-day Poké Stop streak
  • What kind of eggs are acquired from stops
  • Whether eggs will be included in a friend’s gift
  • What Pokémon will hatch from an egg
  • What tasks are acquired from stops
  • What Pokémon will result from completing a research task
  • What items are acquired from stops
  • What Pokémon Team Rocket grunts use
  • What moves Team Rocket’s Pokémon use
  • Which of the Team Rocket grunt’s Pokémon will appear after the battle
  • Whether a trade will be lucky
  • Whether Team Rocket grunts will drop a Mysterious Component

The crane driver mentioned above assuredly knew much of this and did not want to risk missing a rare Pokémon, so he continued to play even while driving.  A 2017 survey of adults who play Pokémon GO found that 27% of players were “likely” or “very likely” to play while driving.  I once spoke to a graduate student who confessed to stopping his car on the highway to capture a particularly rare Pokémon.  

One pair of researchers examined 12,000 car accidents in a county in Indiana - they found that shortly after the game’s introduction, car accidents and fatalities increased disproportionately in areas where Pokémon often appeared compared to areas where few Pokémon were likely to be.  

In order to address this problem, the creators of Pokémon GO added admonishments like “Do not play Pokémon GO while driving.”  In order to play, players must agree to these terms every time they open the game.  

Additionally, when the game detects that the player is moving above a certain speed, it produces a warning message and hides all available Pokémon from the player.  However, it is easy to circumvent this safety precaution by selecting “I’m a passenger.” 

Despite these changes and warnings, many still play while driving through residential areas, where the lower speed prevents the game from recognizing that they are driving.  The fear of missing a Pokémon is so strong that these players are willing to risk their lives or hurt others.  

The DSM 5 lists “Recurrent [substance] use in situations in which it is physically hazardous,” as a sign that a client has a substance use disorder (addiction).  Playing this game while driving is clearly analogous and is directly attributable to its random number generators.  


Pokémon GO is difficult to easily categorize.  Depending on one’s perspective, it can be a blessing or a curse; an engaging hobby or an obsession.  From one perspective, it has created thousands of supportive communities of people who share a common interest.  It has been a godsend for insecure introverts who would not otherwise go outside or engage with others, helping them increase their human interactions and explore the real world.  The game enhances their lives, it isn’t a substitute.

It is also true that for players who are easily attracted or addicted to gambling and other random-number games, Pokémon GO’s design may be particularly devastating, evidenced by those who continue to play even when physically dangerous to do so.  

This helps to demonstrate that video game addiction is different from depression.  Pokémon GO players must leave home, walk around the community, and engage with others to be successful.  The players who risk their lives to play while driving are not hiding from the world or struggling to leave their homes; they’re simply hooked by the random numbers present in nearly all modern games. 


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