In 1964 a young woman was murdered in Queens, New York, and a newspaper told the country that thirty-seven neighbours watched and did nothing. The story became the opening page of nearly every social psychology textbook. It has also, in the decades since, turned out to be wrong in most of the details that made it shocking.
That arc, a vivid story, a famous experiment, a tidy lesson, then a slow correction, is a fair summary of the whole subject. Social psychology asks how the presence of other people changes what one person thinks, says and does. Its best ideas survive. Many of its best-known demonstrations were less clean than the textbooks said. A graduate of this course keeps both: the ideas, and the habit of asking how a classic study was actually done.
Solomon Asch's question was simple: will people state something they can plainly see is false, just because a group does? In his experiments (reported from 1951), a volunteer sat with several others, all but one of them secretly working with the experimenter, and judged which of three lines matched a standard line. The answer was obvious. On 12 of the 18 trials the confederates, one after another, gave the same wrong answer, and the real participant answered near the end.
Alone, people made fewer than 1% errors. In the group, about 36% of answers on the critical trials went along with the wrong majority. About three quarters of participants conformed at least once, and about a quarter never did. That last number is the one textbooks tend to leave out: most answers were still correct, and a survey of textbooks in 2015 found that only one of twenty major texts reported that most responses defied the majority.
The size of the group matters up to a point. A single dissenting-looking companion barely moves people; two or three make a real difference; beyond about three or four the effect levels off. The tool below draws that curve and lets you run a toy group of fifty simulated volunteers.
Curve is approximate and rounded, following the commonly reported shape of Asch's group-size results; secondary sources differ by a point or two. The 50 volunteers are a toy model with a made-up spread of suggestibility (some people never conform), not data.
Without JavaScript: with three or more people giving the wrong answer, about a third of answers conformed in Asch's experiments; with one, only a few per cent.
Why did they conform? Asch interviewed them. Some doubted their own eyes, some knew the group was wrong but did not want to stand out, and a few came to see the lines the group's way. Psychologists later split this into informational influence (the group probably knows something) and normative influence (disagreeing has a social cost). John Turner and colleagues argued that the data fit a third idea better: we follow those we see as "people like us". Conformity also varies by place and time. A 1996 meta-analysis by Bond and Smith, covering 133 studies in 17 countries, found more conformity in more collectivist societies and a decline in the United States over the decades after the 1950s.
In 1961–62 at Yale, Stanley Milgram told volunteers they were helping a study of learning. A "teacher" read word pairs to a "learner" in the next room and gave an electric shock for each mistake, rising in 15-volt steps to 450 V. The learner, an actor, protested and eventually fell silent. If the teacher hesitated, the experimenter in a grey coat gave a fixed series of prods, the first being "Please continue." In the best-known condition, 26 of 40 men (65%) went all the way to 450 V.
The number was shocking, and so was Milgram's reading of it: ordinary people will harm a stranger when an authority tells them to. But Milgram ran many variations, and they are the real finding. Obedience was not a trait of the people; it moved with the situation, from nearly everyone to hardly anyone.
Percentages who went to the maximum 450 V, as reported for Milgram's variations (about 40 participants each). Telephone instructions are often given as 20.5% or 21%.
Without JavaScript: baseline 65%; learner in the same room 40%; learner's hand forced onto the plate 30%; instructions by telephone about 21%; run-down office 47.5%; two fellow "teachers" refuse 10%; a fellow "teacher" who delivers all the shocks 92.5%.
The critics are serious. Gina Perry, who went through Milgram's archive for her 2012 book Behind the Shock Machine, argued that the published account did not match what she found, including that only about half of participants fully believed the shocks were real, and that two thirds of those who did believe disobeyed. Alex Haslam and Stephen Reicher argue that people did not simply obey: they went on when the prod appealed to science ("The experiment requires you to continue") and stopped when it sounded like a bare order. Their reading is "engaged followership": participants identified with the study's goal, not with the learner. A 2009 partial replication by Jerry Burger, which stopped at 150 V for ethical reasons, found rates close to Milgram's at that point. The shock is real; the "people are robots" reading is not.
You see a driver cut across three lanes. You think: what a jerk. When you do it, the exit was suddenly there and the mirror was blocked. Attribution theory, started by Fritz Heider in the 1950s, studies how we explain behaviour: by something in the person (a disposition) or something in the situation. The consistent human habit is to over-read the person. Lee Ross named it the fundamental attribution error in 1977.
The classic demonstrations: in 1967 Edward Jones and Victor Harris had people read an essay praising or attacking Fidel Castro, and told them the writer had been assigned the side. Readers still guessed the writer leaned that way. In Ross, Amabile and Steinmetz's 1977 quiz game, students were assigned by coin toss to write hard questions or to answer them. The questioners looked cleverer to everyone, including the answerers, though the role had made it so.
Harold Kelley's 1967 covariation model gives a tidy rule for reasoning well. Ask three questions about the behaviour: does everyone do it (consensus), does this person do it to everything (distinctiveness), does this person do it every time (consistency)?
Kelley's three textbook patterns are shown; the other five combinations are ambiguous and the model says so. Later studies (McArthur, 1972) found that people tend to under-use the consensus information.
Without JavaScript: low consensus, low distinctiveness and high consistency points to the person; all three high points to the comedian; low consensus, high distinctiveness and low consistency points to the circumstances of tonight.
Culture matters here too. In a well-known study Michael Morris and Kaiping Peng (1994) found that American and Chinese participants explained the same animated fish scene differently, Americans leaning on the fish's inner traits and Chinese participants on the group around it. It fits the larger point that much of social psychology was built on university students in a few rich countries, which Joseph Henrich, Steven Heine and Ara Norenzayan called WEIRD samples (Western, Educated, Industrialised, Rich, Democratic) in 2010.
Common sense says attitudes drive behaviour. A good deal of the time it runs the other way, and Leon Festinger's cognitive dissonance theory (1957) says why: holding two clashing thoughts is uncomfortable, and the cheapest fix is often to change the belief, not the act. The famous test (Festinger and Carlsmith, 1959) had 71 male Stanford students do dull peg-turning, then asked some to tell the next person it was fun, for either $1 or $20. Which group came to like the task more?
Afterwards, who said the boring task had really been enjoyable?
Without JavaScript: the $1 group rated the task as more enjoyable than the $20 group, the opposite of what simple reward would predict.
The $1 group did, and the $20 group only slightly more than people who were never asked to lie. Dissonance theory says $1 is too little to justify the lie, so the mind adjusts the belief; $20 is justification enough. The theory has had rivals (Daryl Bem's self-perception account) and refinements, and the "free-choice" variant, in which people supposedly like what they chose more, has been criticised for a statistical flaw. But the core pattern, that acts shape beliefs especially when we feel responsible for them, is one of the more durable ideas in the field.
On persuasion itself, Richard Petty and John Cacioppo's elaboration likelihood model (1986) says there are two routes: a central one, where people weigh arguments when they are motivated and able, and a peripheral one, where cues such as a confident speaker or a famous face do the work. Strong arguments matter most when people are paying attention. When they are not, packaging does. And attitudes predict behaviour only loosely: Richard LaPiere's 1934 trip with a Chinese couple found almost every hotel and restaurant served them, while most of the same businesses later said by mail that they would not. What people say and what they do can differ.
In the early 1970s Henri Tajfel divided schoolboys in Bristol into two groups by a trivial rule (they were told it was a preference for paintings by Klee or by Kandinsky) and then asked each boy to hand out points to anonymous members of the two groups. The boys knew none of them and would gain nothing. Yet they favoured their own group, and often chose options that gave their group fewer points in total as long as the gap over the other group got bigger. This minimal group paradigm underlies social identity theory: part of who we are comes from the groups we belong to, and we want our group to look good against others.
You are in the "blue" group. Choose one column: points for an anonymous blue member (top) and an anonymous "green" member (bottom).
An invented matrix in the spirit of Tajfel's, not his actual numbers. Real participants were schoolboys, and what they picked on matrices designed to pull the strategies apart is what the study reported.
Without JavaScript: in the matrix, giving 13 points to both groups gives each 13; giving 7 to your group and 1 to the other leaves a gap of 6 but costs your group 6 points.
Muzafer Sherif's Robbers Cave study (Oklahoma, 1954) is the famous other half: twenty-two boys at a summer camp, split into two groups, competed for prizes and soon despised each other, then made peace when forced to cooperate on shared goals. The conclusion that competition breeds hostility and common goals reduce it is widely taught. The critique is that the story is tidier than the record: earlier versions of the study in 1949 and 1953 did not produce the same result (in one, the boys turned on the experimenters), and Michael Billig has argued that the staff were effectively a third group steering events. What has held up better is Gordon Allport's 1954 contact hypothesis: contact between groups reduces prejudice under conditions such as equal status and shared goals, supported by a large meta-analysis of hundreds of studies by Thomas Pettigrew and Linda Tropp.
Some newer popular ideas deserve caution. The Implicit Association Test is widely used to measure unconscious bias, but its scores are only modestly stable from one session to the next and predict individual behaviour weakly, and changing a score has not reliably changed behaviour. It may tell you about group-level patterns better than it tells you about a person.
The Kitty Genovese story, as taught for decades, said thirty-eight people watched a murder from their windows and did nothing, out of apathy. In 2007 Rachael Manning, Mark Levine and Alan Collins went back to the record: far fewer people had a clear view, many who heard noise did not realise what was happening, and at least one person called the police. In 2016 the New York Times itself called its original reporting flawed and said it had grossly exaggerated the number of witnesses.
The better evidence is laboratory. In 1968 John Darley and Bibb Latané had students talk by intercom, one at a time, with others in separate rooms; one of the "others" seemed to have a seizure. Students who believed they were the only listener reported it before the fit ended 85% of the time. With one other possible listener the figure was 62%, and with four others, 31%. Latané and Darley called the mechanism diffusion of responsibility: with others around, each person feels less personally responsible.
The 85, 62 and 31 are from Darley and Latané (1968), the proportion reporting before the fit ended. The "someone helps" row is arithmetic that assumes each listener acts independently, which real groups, who also watch each other, will not.
Without JavaScript: each person is less likely to act in a group (85%, 62%, 31%), but if five listeners each had a 31% chance, the chance that at least one acts is about 84%, close to the lone person's 85%.
Look at what the arithmetic says. The effect is real for each individual, but the group as a whole may still produce help about as often as one person would. That is why later work added caveats. A 2011 meta-analysis by Peter Fischer and colleagues found the bystander effect strong in non-dangerous emergencies and weaker in dangerous ones, and weaker when bystanders are not strangers. A 2020 study by Richard Philpot and colleagues of more than 200 real CCTV recordings of street conflicts in the UK, the Netherlands and South Africa found that in over 90% someone intervened, and more bystanders meant more chance of help. The bystander effect is real, but people are not generally apathetic.
The Open Science Collaboration (2015) tried to repeat 100 psychology studies; about 36% of the repeats were statistically significant against 97% of the originals, and the repeats showed effects about half the size. Social psychology fared worse than cognitive psychology (about a quarter replicated against about a half). Treat the list below as a rough report card, not a verdict on any one study.
Held up well:solid Asch-style conformity in its broad direction; anchoring-like context effects; the contact hypothesis; the bystander effect in non-dangerous settings.
Held, but smaller or messier:shrank Milgram's obedience (the rate depends on setup, and the interpretation changed); cognitive dissonance in its simplest forms; the fundamental attribution error (strong in the lab, culture-bound in size).
Failed or collapsed:failed Many social-priming effects, such as words about old age making people walk slower; power posing changing hormones; ego depletion. See Research Methods in Psychology (35/19).
Disputed:disputed The Stanford Prison Experiment, which lasted six days in 1971, said guards turned cruel by role. Thibault Le Texier (2018) reported from the archive that the guards were coached on how to behave, so it is better read as a demonstration of what people do when told what is expected than as evidence of a natural tendency.
Other people shape what we say, do and believe, and the situation can matter more than character. But the best-known demonstrations are more qualified than their reputations: most people resisted in Asch's rooms, Milgram's results depended on the setup, the Genovese crowd was exaggerated, and several famous effects shrank on re-testing.
Try this: the next time someone's behaviour annoys you, write down two situational explanations before you settle on a trait.
Sources. Asch, "Opinions and Social Pressure," Scientific American 1955, and the 1951 monograph (about 36% of critical responses conforming; about 74% at least once; control error under 1%); a 2015 survey of twenty textbooks on Asch (and an earlier one in 1990); Turner on referent informational influence; Bond and Smith, Psychological Bulletin 1996. Milgram, Journal of Abnormal and Social Psychology 1963 and Obedience to Authority (1974): variations as summarised in Wikipedia, "Milgram experiment"; Perry 2012; Haslam, Reicher and Birney on engaged followership; Burger, American Psychologist 2009. Jones and Harris 1967; Ross 1977; Ross, Amabile and Steinmetz 1977; Kelley 1967; McArthur 1972; Morris and Peng 1994; Henrich, Heine and Norenzayan, Behavioral and Brain Sciences 2010. Festinger and Carlsmith, 1959 (71 male Stanford students); Petty and Cacioppo 1986; LaPiere 1934. Tajfel, Billig, Bundy and Flament, "Social categorization and intergroup behaviour," European Journal of Social Psychology 1971; Sherif et al., Intergroup Conflict and Cooperation: The Robbers Cave Experiment (1961); Billig; Allport, The Nature of Prejudice (1954); Pettigrew and Tropp, 2006. Darley and Latané, Journal of Personality and Social Psychology 8 (1968), 377–383; Manning, Levine and Collins, American Psychologist 2007; the New York Times acknowledgement of 2016; Fischer et al., Psychological Bulletin 2011; Philpot et al., American Psychologist 2020. Open Science Collaboration, Science 2015; Le Texier, American Psychologist 2019. Calculations on this page (the 84% and 85% group figures, the toy simulation) were run in node. This piece describes research and is not a guide to any individual's behaviour.