The Barnum effect is our tendency to apply personal meaning to statements that could apply to many people.

For statements such as the results of a personality test, the effect is stronger if:

they are sufficiently vague — handy phrases include "at times," "a tendency to," "some of," etc.

they are mostly positive — we're more inclined to accept positive evaluations of ourselves than critical ones

You may recognise these tricks from a horoscope or your star sign, magicians, fortune-tellers, fortune cookies, con artists and, perhaps, marketing. There's a fascinating magician's technique you may have seen called cold reading that uses the Barnum effect with other tricks ("I see someone with heart pain in your family.") to make it seem like they know a lot of personal details about someone at a first meeting.

Originally from Bertram Forer, who called it "the fallacy of personal validation," it was later known as the Forer effect until Paul Meehl suggested it should be named the Barnum effect after P. T. Barnum (now of The Greatest Showman fame) for the way he could easily fool an audience with these techniques and to emphasize that we should all know and be on the lookout for being fooled. For that reason, I called it the same here.

Bertram Forer ran an experiment with his students (pdf), giving everyone the same results for their individual personality assessment. Generally, the students all thought the same description applied very well to themselves. He used these statements taken "largely from a newsstand astrology book":

You have a great need for other people to like and admire you.

You have a tendency to be critical of yourself.

You have a great deal of unused capacity which you have not turned to your advantage.

While you have some personality weaknesses, you are generally able to compensate for them.

Your sexual adjustment has presented problems for you.

Disciplined and self-controlled outside, you tend to be worrisome and insecure inside.

At times you have serious doubts as to whether you have made the right decision or done the right thing.

You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations.

You pride yourself as an independent thinker and do not accept others' statements without satisfactory proof.

You have found it unwise to be too frank in revealing yourself to others.

At times you are extroverted, affable, sociable, while at other times you are introverted, wary, reserved.

Some of your aspirations tend to be pretty unrealistic.

Security is one of your major goals in life.

I learned about it from a discussion of the Meyers-Briggs test (I'm an ENTP btw).

Here's Paul Meehl advocating for the Barnum effect:

"Many psychometric reports bear a disconcerting resemblance to what my colleague Donald G. Paterson calls “personality description after the manner of P. T. Barnum” ... I suggest—and I am quite serious—that we adopt the phrase Barnum effect to stigmatize those pseudo-successful clinical procedures in which personality descriptions from tests are made to fit the patient largely or wholly by virtue of their triviality; and in which any nontrivial, but perhaps erroneous, inferences are hidden in a context of assertions or denials which carry high confidence simply because of the population base rates, regardless of the test’s validity. I think this fallacy is at least as important and frequent as others for which we have familiar labels (halo effect, leniency error, contamination, etc.). One of the best ways to increase the general sensitivity to such fallacies is to give them a name. We ought to make our clinical students as acutely aware of the Barnum effect as they are of the dangers of countertransference or the standard error of r."

Meehl, P. E. (1956). Wanted—a good cook-book. American Psychologist, 11(6), 263–272. https://doi.org/10.1037/h0044164

The Barnum effect

The isolation effect is our tendency to remember an item that stands out in some way from a set of otherwise similar items—you might easily guess, for example, which name we are more likely to remember from a list of Tom, Terry, Angelica, Theo and Tyler.

When presenting information, the isolation effect is practical if you wish to draw attention to specific items. By standardising the presentation of other items in a list, maybe by muting the colours, making them the same size, or removing features that stand out, you can draw people's attention and improve people's memory of your chosen items.

The isolation effect is standard in web design by using distinctiveness: red notification bubbles on a set of otherwise homogenous apps, a "most popular" plan more prominent than the other options, or a Call-To-Action (CTA) button in a contrasting colour.

The isolation effect is also known as the Von Restorff effect after the German psychiatrist Hedwig von Restorff. See, for example, Hunt, R.R. The subtlety of distinctiveness: What von Restorff really did. Psychonomic Bulletin & Review 2, 105–112 (1995) for a summary of Von Restorff's most cited paper on the effect.

The isolation effect

The Rhyme As Reason Effect suggests that we're more likely to consider something as accurate or truthful when it rhymes. In a lovely study that asked people to consider the accuracy of both rhyming and non-rhyming aphorisms, "Woes unite foes," or "What sobriety conceals, alcohol reveals," for example, were considered more accurate than "Woes unite enemies," or "What sobriety conceals, alcohol unmasks."

A classic example outside of old sayings is OJ Simpson's trial where the defense attorney memorably noted "If the gloves don't fit, you must acquit!"

You can read the study in the delightfully titled paper, Birds of a feather flock conjointly: Rhyme as Reason in Aphorisms (pdf), by Matthew McGlone and Jessica Tofighbakhsh.

In a related note I was always curious how "Beer before wine, you'll feel fine," tallied up with what I heard in the US: "Beer before liquor, never been sicker," or even "Grape or grain but never the twain." It turns out from a neat 2019 study that, whichever way round you rhyme them, they have no effect on your hangover despite how persuasive the Rhyme As Reason effect may be — even after a few beers.

The Rhyme As Reason Effect

The curb-cut effect illustrates how when we design to benefit disadvantaged or vulnerable groups we end up helping society as a whole.

Angela Glover Blackwell explains how campaigning by students with disabilities in Berkeley in the early 1970s led to adding curb cuts to the Berkeley sidewalks to make access easier for those in wheelchairs. Yet it wasn't just people in wheelchairs that it helped. Curb cuts also made life easier for people pushing children in strollers, people using trolleys for deliveries, people pulling a suitcase, those wheeling bikes or on skateboards, and it also helps save lives by guiding people to cross at safe locations.

Another example is adding closed captioning to TV that helps anyone watch in a noisy bar, a waiting room, or watching an airline safety video. Or a classic example of universal design in the OXO Good Grips range originally made to be comfortable for holding a peeler even if you have arthritis.

It's also a useful analogy for "how laws and programs designed to benefit vulnerable groups, such as the disabled or people of color, often end up benefiting all," (PolicyLink) whether that be increasing broadband access, improving public transport or taking cuts out of curbs.

Here's a short, fun video of Gary Karp explaining the curb-cut effect.

Thanks to my patron Quintin Balsdon for sharing it with me.

The curb-cut effect

In much of life we're used to things adding up — got one scoop of ice cream? Two is likely to be better. Buying one thing? Getting another free is probably a good thing. The dilution effect, however, illustrates an interesting action of our brain when evaluating our options. Niro Sivanathan showed that when displaying possible side-effects of drugs, if you were to add another side-effect, a minor one like 'itchy feet', instead of the extra negative side-effect increasing our overall perception of the risk of the drug it actually lowered it. So, people would deem a drug with the side effects heart attack, stroke, and itchy feet, as less risky than one with just heart attack and stroke.

In another clever experiment by Christopher Hsee at the University of Chicago, people were willing to pay less for a new dinnerware set when the set was actually larger but also included some broken items. Even though a set had more intact items the presence of a few broken ones decreased the set's perceived value.

And the same may be true when making an argument to persuade someone to see our point of view. If you have 2 strong points and 1 weaker one, your argument may actually be made weaker by adding the extra point. As Niro Sivanathan, an Associate Professor of Organisational Behaviour at London Business School, explains: Arguments don't add up. They average out.

Next time you're making your case, consider sticking to your strong arguments.

Hear Niro Sivanathan explain the dilution effect in his 10 min TED talk The counterintuitive way to be more persuasive

The paper: Sivanathan, N., Kakkar, H. The unintended consequences of argument dilution in direct-to-consumer drug advertisements.Nat Hum Behav 1,797–802 (2017).

The dilution effect

There are a lot of reasons why it can make sense to go with the majority. Going with the popular view is a shortcut for taking the time and effort to make our own decisions from scratch. We might reason that if others believe it, then it's probably true. But we can also keenly feel the desire to conform to the majority view because it's uncomfortable to hold a different opinion — the easy choice is so often to go with the flow even if, deep down, you disagree. So we get the bandwagon effect.

The bandwagon effect can lead to the Abilene paradox — where a group can make a decision that no one in the group agrees with. On a night out it may lead to just following the crowd, but in a company it could lead to launching a product that no one thinks is good or, more seriously, in safety critical industries like airlines, if people don't feel comfortable speaking up against the group or authority it could lead to accidents.

The bandwagon effect

The essence of the bystander effect is that in a situation where someone needs help, if others are around who could help, then it discourages us as individuals from stepping in.

While there may be many reasons for this, and it has been replicated in many different contexts, a recent study of CCTV footage paints a more optimistic picture. In the study, they saw that although the likelihood of any individual intervening may be reduced with other bystanders present, the chances of someone coming to help increase the more people are around. In 9 out of 10 public conflicts they studied at least one person, and often several, came to help. So the lady in the sketch would probably be OK.

Given the bystander effect, I remember being taught that if you are in a motor vehicle accident, don't assume that someone has called for help already: it could help to choose someone directly and ask them to call for help to avoid everyone thinking everyone else will do it.

It reminds me of the story about four people named Everybody, Somebody, Anybody and Nobody (also known as the responsibility poem):

There was an important job to be done and Everybody was sure that Somebody would do it. Anybody could have done it, but Nobody did it. Somebody got angry about that, because it was Everybody’s job. Everybody thought Anybody could do it, but Nobody realized that Everybody wouldn’t do it. It ended up that Everybody blamed Somebody when Nobody did what Anybody could have.

The paper referenced is: Philpot, Richard & Liebst, Lasse & Levine, Mark & Bernasco, Wim & Lindegaard, Marie. (2019). Would I be helped? Cross-national CCTV footage shows that intervention is the norm in public conflicts. The American psychologist. 75. 10.1037/amp0000469. (pdf)

The Bystander Effect

Have you ever noticed the pull of completing the last few pieces of a jigsaw puzzle? Or maybe it’s the last clue of a murder mystery, the final chapter of your book or the ultimate mile of a marathon. Being close to our goal can motivate us to get to the end. That’s the goal-gradient effect at work.

The goal-gradient effect—also known as the goal-gradient hypothesis—may be part of why getting started is sometimes the most challenging part and may cause us to over-prioritize near-term goals to the detriment of later ones.

In the example in the sketch, Oleg Urminksy and coauthors found that as people approached the final stamp of a loyalty card towards a free coffee, they were more likely to buy coffee faster. And when issued with a new card, the rate of purchase dropped. The urgency diminished with the blank card and the perk once again distant.

The researchers also found that it wasn’t the absolute distance from a goal but the perception of distance that mattered. People who started with a 12-stamp card with two stamps already completed tended to complete the card faster than those who started with an empty 10-stamp card, even though they had the same number of stamps to the goal. This related quirk of behavior is known as the endowed progress effect or the progress illusion.

Read more in Katy Milkman and Kassie Brabaw's Scientific American article, Why Feeling Close to the Finish Line Makes You Push Harder.

Related Ideas to The Goal-Gradient Effect

Katy Milkman also educated me about the fresh start effect

This sketch appears in my book Big Ideas Little Pictures

The goal-gradient effect

The overview effect is the ultimate example of "seeing the forest for the trees." It’s the realisation that we live on a fragile planet, that we are all connected, and that this is all we’ve got—our one and only home.

Coined by author Frank White, this phenomenon is most vividly experienced by astronauts, who return to Earth profoundly changed by seeing our planet from space. Their reflections highlight the emotional and philosophical impact of this shift in perspective:

“You develop an instant global consciousness, a people orientation, an intense dissatisfaction with the state of the world, and a compulsion to do something about it. From out there on the moon, international politics look so petty.”
— Edgar Mitchell, Apollo 14 astronaut

“When we look down at the earth from space, we see this amazing, indescribably beautiful planet. It looks like a living, breathing organism. But it also, at the same time, looks extremely fragile … Anybody else who’s ever gone to space says the same thing because it really is striking and it’s really sobering to see this paper-thin layer and to realize that that little paper-thin layer is all that protects every living thing on Earth from death, basically. From the harshness of space.”
— Ron Garan, Shuttle/ISS astronaut

This sketch is inspired by the iconic photograph of Earth taken from the moon during the Apollo 11 mission. The image captures the striking beauty and fragility of our planet and perfectly embodies the spirit of the Overview Effect.

The Overview Effect A Profound Shift in Perspective

The story goes something like this. Back in colonial India the top Brit in charge decided there were too many cobras around Delhi. To reduce the population they put in place a cash reward, or bounty, for anyone who brought in a dead cobra. The intention was clear. Legend has it that people did bring in the cobras reliably because some enterprising souls had started breeding cobras for the very purpose of getting the bounty. When the authorities realised this they scrapped the scheme, the cobra farms closed and the bred cobras were released into the wild significantly increasing the cobra population by a few orders of magnitude. Hence, the cobra effect: when a well-intentioned measure can have the opposite effect to that desired.

It’s not clear how true this story is, but the cobra effect has been demonstrated many times. The Freakonomics podcast on the cobra effect discusses some excellent examples (with references), including:

A bounty on rats in French colonial Hanoi — where the bounty was earned by bringing in a rat tail — which went the same way as the cobra story

Removing wild pigs at Fort Benning, Georgia, at $40 a pigs tail that didn’t make a dent. It could be the hunters would bait the pigs with all sorts of tempting scraps. Many pigs learned to avoid the hunters and instead bred like crazy while well-fed on scraps.

The capital of Colombia, Bogotá, tried to reduce traffic congestion by restricting each car from driving one day during the week. The result: people started buying more than 1 car and did more driving on weekends.

Publication of proposed areas of habitat to be protected for endangered species meant land developers responded by building in those areas before the land was protected.

People are smart. Incentives work—in the sense that you tend to get what you incentivise. So be careful what you are incentivising. As Charlie Munger said: "Show me the incentive, and I'll show you the outcome."

The cobra effect

The 3-day effect is the name give to what happens to us after being out in Nature for 3 days or more. Something about it resets us and improves our mood, our wellbeing, and how well our brain is working.

Observed by river rafting guide Ken Sanders who used to see a marked change in the groups he led on the 3rd day of being out on the river, it’s known as the 3-day effect. Since then, David Strayer and his group at the University of Utah have conducted studies that measured a real change in our calmness and even our creative problem-solving after 3 or more days in Nature.

“I think it takes the first two days and nights to wash away whatever veneer of civilization you have brought with you. The new reality begins on that third day.”

More about the 3 day effect at National Geograhic: This is your brain on Nature and REI: The Nature Fix.

No doubt similar things at work to the magic of forest bathing.

The 3-day effect

The Diderot effect describes how new purchases can lead to a negative spiral of replacing possessions that no longer live up to the new standard. In a capitalist or consumerist society, it highlights the dangers of material possessions on ourselves and our finances.

"Regrets on Parting with My Old Dressing Gown."

The effect is named after 18th-century French philosopher Denis Diderot, who wrote the entertaining and unusually-titled essay "Regrets on Parting with My Old Dressing Gown."

In the essay, Diderot relates how his possessions no longer seemed up to scratch after being given a flashy new scarlet dressing gown. Seeing this, he replaced his old straw chair with a leather one, a plank bookshelf with an inlaid armoire, a clay statue with a bronze statue, and so on. In the process, he emptied his carefully earned savings.

His tale is an example of the Diderot Effect in action.

What's more, Diderot complains that whereas he was the master of his old dressing gown, he became a servant to the new one, needing to guard it from his clumsiness, spills, or burns. Our possessions can begin to control us rather than us control them.

More generally, the effect also highlights that we surround ourselves with objects that fit our sense of identity. When we receive something that reflects a new, aspirational identity, rather than rejecting the new thing, we may find ourselves replacing our old objects and selves to fit the new.

Sometimes, we may be excited about embracing a new identity. Clearing out items reflecting our old selves may be a blessing and reflect aspects of our lives we wish to leave behind. Yet it perhaps pays to consider whether it's driven by the products or ourselves—whether we're still the masters or whether they are.

As I learned from Dev Patnaik, products are created by culture and create culture.

Here are some examples of the Diderot Effect in action that I could relate to:

Denis Diderot gradually replacing his possessions with fancier more expensive ones and becoming poor as a result.

Replacing my hastily bought student furniture with smarter furniture for our own home.

Adding a new smart painting to a wall causing you to take down your old music posters.

A new pair of shoes causing me to reconsider the whole outfit.

Cultural anthropologist Grant McCracken introduced the Diderot Effect, which I learned about from James Clear's Atomic Habits. As I learned from Seth Godin's Akimbo podcast episode — The Deletionists, Diderot also played a key role in the development of the encyclopedia.

The Diderot Effect appears in my book Big Ideas Little Pictures.

Here's a translation of Denis Diderot's essay "Regrets for my Old Dressing Gown, or

A warning to those who have more taste than fortune"

The Diderot Effect

The Rashomon effect is the name given to situations where people give mutually contradictory versions of the same event. 

Named after the 1950’s Japanese film Rashomon—widely seen as a masterpiece—which hinges on four conflicting descriptions of the same incident.

Also commonly seen on the football field by coaches after the game.

The Rashomon effect

I like the spotlight effect because it basically shows that most of us can just relax a bit and not stress about what other people think — because they’re probably not thinking about us, they’re probably thinking about themselves.

I probably only remember it because of the effect effect

The spotlight effect

The effect effect is the undoubted extra stickiness and shareability of an idea by calling it an effect.

There’s something about summing up a piece of research or an observation with the name effect that makes it a whole lot easier to communicate and remember.

The more solar panels installed in a neighbourhood the greater chance of a growth of solar panels in that neighbourhood

And, for those of you wondering why it’s not the affect affect, here's a sketch explaining when to use affect vs effect

Perhaps because of the effect effect, I've covered a lot of effects already in sketches (though there are many more to do). See all "effect" sketches

The Effect Effect

Lake Effect Snow is a phenomenon where crazy amounts of snow can fall in massive storms on a lake’s downwind—leeward—side. Where the effect is pronounced, to the east of some of the Great Lakes in the U.S. (think Buffalo), it’s responsible for the regions known as the snow belt.

It works like this: Cold air blows over a lake. As the cold air passes over the warmer lake, it picks up water vapor from the water, which warms the air. This causes the air to rise and, in turn, cool, such that when it reaches the downwind side of the lake, it has become cold and moist. This simple change can lead to some incredible snowstorms dumping 2 to 3 inches of snow per hour. Satellite pictures show it in action pretty clearly.

If there is a rise in land elevation along the path of the cold air, the air can cool faster and increase the effect — and also cause a rain shadow. And if there’s a lot of convection and the air rises quickly, you can even get what’s called thundersnow—a thunderstorm in a snowstorm.

Find the weather interesting? Me too. Also see:

Yesterday’s weather (applying weather forecasting to productivity forecasting)

Know your cirrostratus from your altocumulus

For everyday weather-related phenomena explained, see Dennis Mersereau’s The Skies Above: Storm Clouds, Blood Moons, and Other Everyday Phenomena, Mountaineers Books (2022). Dennis is also the source of the lovely phrase Nature’s greatest snow machine.

Lake-effect snow

The Streisand effect describes what happens when you try to censor or suppress information: it draws attention to it.

It’s named Streisand after Barbara Streisand tried to have an aerial photo of her house removed from a set of California coastline photos intended to document coastal erosion. Views of the photo apparently went from 6 to 420,000.

The Streisand Effect as a term was coined by Mike Masnick

The Streisand Effect

The singularity effect is the name for how we care disproportionately about an individual as compared to a group.

Think Saving Private Ryan, where an enormous effort is launched to save a single soldier in the Second World War.

It turns out that even as you add a second person, there’s some justification for something known as compassion fade. The addition of more people doesn’t increase our willingness to help proportionally — our compassion fades as more people are involved.

The singularity effect

The nocebo effect is how the expectation of pain or negative effects of a treatment increases the chances people will feel them — even if they're aren't any. So, tell someone that a treatment will hurt or have side-effects and they're now more likely to feel that pain or find something wrong.

Taken together with the placebo effect I guess we might do well, for normal affairs, to let people know that what they will get will probably help them and not raise unnecessary expectations that something might hurt.

The nocebo effect

The placebo effect is the remarkable yet commonplace fact that when people expect a treatment to help, it can, even if the treatment doesn't actually do anything.

The placebo effect

The Fresh Start Effect explains why we’re more likely to tackle meaningful goals or form new habits at the start of a day, week, month, or year. 

These fresh beginnings—like a birthday, moving to a new house, or even a Monday morning—are powerful mental triggers that motivate us to take action and start anew.

It’s fascinating how the simple act of marking a “start” can make us more open to change and new challenges. Whether it’s the first day of the year or the start of a new chapter in life, these moments provide a sense of renewal and opportunity.

We explored this idea on the podcast: Listen to The Fresh Start Effect on the Sketchplanations podcast

You can also hear about it from Katy Milkman herself, Professor at The Wharton School of the University of Pennsylvania, on the Freakonomics podcast: When Willpower Isn’t Enough.

The fresh start effect

The IKEA effect is the increase in value we feel towards self-made products—products that required our effort to create them. Or, less formally, we love it more if we made it.

The effect is named after the odd sense of satisfaction many of us feel after spending more time and sweat than expected putting together IKEA's famous flat-pack creations. Yet not only does more effort equal more love. If we've put effort into something ourselves, we're also more likely to, often mistakenly, think that others will value it more, just as we do.

Together with others, Dan Ariely, a professor of behavioral economics, conducted several experiments leading to these conclusions.

Ariely also points out that kids are the ultimate expression of the IKEA effect: they're very hard, don't come with instructions and take a lot of effort.

Watch Dan Ariely do a great job explaining some experiments that lead to this conclusion, or read the full paper, The “IKEA effect”: When Labor Leads to Love (pdf), Norton, Mochon, Ariely HBS working paper, 2011.

The Betty Crocker Effect, or ‘the egg theory.’

The IKEA effect

Where “all the children are above average.” From the intro by Garrison Keillor to the News from Lake Wobegon on the radio show A Prairie Home Companion. Also known as illusory superiority. From the popular studies where, for example, 80% of people think they are above average drivers, when asked to estimate the % of chores done in the household it adds up to more than 100%, and we overestimate our input to project work and it’s impact on its success. For the best treatment I’ve read, and references, see Thinking Fast and Slow by Dan Kahneman.

The Lake Wobegon Effect

When cliques, of people, with a lot of time to chat, start to believe in things that would seem crazy to the wider population. So named after an observation of firemen who would spend a lot of time talking between fires.

My intro to this was from Fooled by Randomness by Nassim Nicholas Taleb.

The Firehouse Effect

The Betty Crocker effect refers to how, in the world of instant cake mixes, when something is too easy, it reduces the value.

The legend goes that instant cake mixture that just needed water didn't sell nearly as well as when you needed to add an egg. Adding the egg yourself gives investment in the process of making the cake, so we appreciate it more, and the extra effort demonstrates the act of love that is baking a cake.

As is so often the case, Dan Ariely explains it well. 20mins well spent watching Dan Ariely's TED talk What makes us feel good about our work?. You can jump straight to it around 12mins 50s.

Effect sketches