BiasesSocial
Bandwagon Effect
Also called Social proof · Herd behavior · Conformity bias
Believing or doing something because many other people seem to believe or do it.
Definition
The bandwagon effect is the pull to adopt a belief or behavior because it seems popular, rather than because of the evidence for it.
As a reasoning error, it’s sometimes called the appeal to popularity: “everyone thinks so, so it must be true.” As a bias, it works more quietly. We rarely decide to follow the crowd. We just find that the popular option seems more plausible, more attractive, or safer.
How it works
In Solomon Asch’s experiments in the 1950s, people judged which of three lines matched a reference line, a task almost everyone gets right alone. But when seated with actors who all gave the same wrong answer, participants went along with the group on about a third of those trials, and roughly three-quarters went along at least once.
A 2006 study by Matthew Salganik, Peter Dodds and Duncan Watts showed the same pull at scale. More than 14,000 people downloaded unknown songs. In some groups, people could see how many times each song had been downloaded. Showing popularity made success far more unequal and much less predictable: which songs became hits depended heavily on early, partly random downloads, not just on quality.
How to spot it
“Everyone’s buying it,” “everyone agrees,” or “nobody believes that anymore” is the main reason offered.
Your interest in something jumped after you saw how many others liked it.
Your opinion shifted after learning what most people around you thought, without new evidence.
Poll numbers or “momentum” are treated as arguments for a candidate or policy.
Disagreeing feels awkward in a way that has nothing to do with the arguments.
Examples
01Campaign momentum
A candidate’s supporters argue that voters should back them because they’re surging in the polls and are the one to beat. The opposing campaign says the same thing a few weeks later, when the polls flip.
What went wrong
A candidate’s popularity says something about their chance of winning, which matters for strategic voting. It says little about whether they’d be good at the job. Campaigns on every side lean on momentum because it works.
02The meme-stock rush
In early 2021, shares of a struggling video-game retailer shot up as millions of retail investors piled in, many because they saw everyone else doing it. The price later fell sharply, and many late buyers took heavy losses.
What went wrong
Rising prices and online excitement were treated as evidence of value. Some early buyers did well, but for later buyers, the crowd was a signal of how many people had already bought, not of what the company was worth.
03The bestseller label
A shopper picks the book marked “#1 bestseller” over the one they actually came in for.
What went wrong
Probably nothing too serious, since popular books are often good. But the label measures sales, not fit, and the shopper’s own preference got overridden by someone else’s.
Why we do it
Following the crowd is often smart. When you don’t know which restaurant is good, a busy one is a decent bet. People also care about belonging, and agreeing with the group is safer socially than standing apart. The trouble comes when popularity replaces evidence entirely, and when everyone is following everyone else, so nobody is actually checking.
Check yourself
1Separate popularity from evidence
Ask whether the reason you believe something would survive if it were unpopular.
If most people thought the opposite, would my reasons still convince me?
2Ask why others believe it
Popularity is only as good as the reasons behind it. Find out whether the crowd is following evidence or following each other.
Did these people each look into it, or are they mostly copying each other?
3Notice the timing
Check whether your view changed when you learned the numbers, not when you learned something new about the issue.
What changed my mind: new information, or finding out what everyone else thinks?
When the shortcut is reasonable
Relying on what others think is often rational. A strong consensus among independent experts who have examined the evidence is a good reason to believe something, which is why scientific consensus matters. Crowd choices also carry real information, like which apps actually work or which roads are busy.
The key is independence. A crowd of people who each checked the evidence is a strong signal. A crowd of people copying each other is just one opinion repeated many times. The bias is treating the second kind of crowd as if it were the first.
Sources & further reading
- Solomon E. Asch, “Opinions and Social Pressure,” Scientific American 193, no. 5 (1955): 31–35.
- Matthew J. Salganik, Peter Sheridan Dodds and Duncan J. Watts, “Experimental Study of Inequality and Unpredictability in an Artificial Cultural Market,” Science 311 (2006): 854–856.
- Robert B. Cialdini, Influence: The Psychology of Persuasion (William Morrow, 1984). The classic account of “social proof.”
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