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Health, Sports & Psychology
  • Video
  • 5 mins
  • Level 1: Introductory

Bystander intervention

Updated Friday 9th April 2010

Dr Jovan Byford, Lecturer in Psychology at the Open University guides us through bystander intervention and the factors that affect our behaviour during unusual situations.


Copyright The Open University


Copyright The Open University


Jovan Byford: Psychologists have been interested in bystander intervention for more or less forty years now and the interest was sparked by a real life event, the murder in 1964 of a young woman called Catherine Genovese who was killed one night in New York as she returned from work.

Now murders in New York suburbs were not particularly rare in those days but one thing that captured the public imagination, and also attracted newspaper headlines, was the fact that subsequent police investigation revealed that as many as thirty-eight witnesses were present when she was killed, or rather thirty-eight of her neighbours noticed that an attack was taking place in the street, and yet none of them intervened in a way that would prevent her killing.

Out of the thirty-eight witnesses only one of them screamed, “Leave the girl alone!” from the window, while another one called the police but did so after it was already too late and Catherine Genovese was dead.

And after this event two psychologists, Bibb Latane and John Darley, decided to investigate why people didn’t intervene in that case and they decided essentially to start to embark on a research project on bystander intervention.

And their starting premise was that in everyday life we often find ourselves in the position of a bystander. We might witness somebody’s car breaking down, we might witness a medical emergency, somebody fainting in the street, we might witness a petty crime or a fire, or any kind of emergency situation like that.

And Latane and Darley argued that in some situations people do intervene and help, in others they don’t. And what they wanted to find out is what determines whether somebody will help or won’t. In other words, they wanted to look at what are the aspects of the particular situation that will either inhibit or facilitate bystander intervention.

And in order to investigate this issue they conducted a series of very clever psychological experiments in the laboratory. The main feature of these experiments is that they took place in a very controlled environment which enabled them to manipulate very small aspects of the situation and then observe and measure how that affects people’s likelihood to intervene.

So what they did is they conducted, or rather they staged a number of emergencies - whether somebody experiencing an epileptic fit, a fire or somebody falling off a ladder, and they looked at in what situations people will intervene and in which they won’t.

Now one key study that I will describe in more detail is one that they called the lady in distress experiment. What they did essentially is they invited students from the university where they worked to come to a laboratory on the pretext that they would take part in a piece of market research.

Once they arrived to the laboratory they were met by a young woman who gave them a bogus questionnaire - all this was just a deception, a pretext of getting them into the laboratory. As they sat in the room and filled in this bogus questionnaire the woman left the room and they could hear her working next door, and as they were filling in this questionnaire they would hear the following situation: They would hear the woman looking through the drawer, climbing up a chair or a step ladder, and then they would hear her fall. The fall was followed by her screams and cry for help.

And what Latane and Darley were interested in is basically how many of the participants who took part in the study individually would actually go and intervene in some way, call for help, go and offer their assistance, etc.

And what they found is that in 70% of the cases out of the thirty people who took part in the experiment and repeated this procedure, twenty-one people intervened which suggested that when people were alone in the room, or rather when people were the only bystander present they are quite likely to intervene. In 70% of the cases they would intervene, in line with a social norm that people should offer somebody help when they’re in distress.

But then they manipulated the experimental situation further and what they did is then, rather than having one person arrive to the laboratory and fill this bogus market research questionnaire, they had two people do it. Two naïve participants would come along and do it, and they were met again by this same woman who was the confederate of the experimenters and who was part of the deception, and then they would repeat exactly the same procedure except this time there were two people in the room.

And their prediction was that actually in this situation it was even more likely that people will intervene, because if most people intervene then the likelihood of getting two people who won’t in the room at the same time should actually be smaller. So in this case they predicted that people would be more likely to intervene. But what they found is that this was not the case. In fact, in this instance in only 40% of the cases did one of the participants actually go and help the woman. In other words, what they showed is that just the presence of one other person in the room reduces the likelihood of somebody intervening from 70% to just 40%.

In the final condition that they did they actually, rather than putting two naïve participants in the room they actually put one participant and one stooge, another confederate of the experimenters who was pretending to be a participant, he too was filling out the bogus questionnaire but was instructed in advance not to do anything, in other words to ignore the emergency.

In this situation only 10% of participants actually went and helped the woman. In other words, being in the presence of a passive bystander, somebody who doesn’t intervene, reduces the likelihood of intervention from 70% to just 10%. This finding that just the presence of another person reduces the likelihood of intervention has become known as the bystander effect.

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