Irrationality – the example of the police lineup

Why do people (them, you, I) behave irrationally?

There are many famous social psychology experiments which demonstrate mob-mindedness, self-delusion, etc.

Psyblog has a post well worth downloading. In it he links to a series he has written on 10 “brilliant social science experiments”:

1. The halo effect – Nisbett
2. Cognitive dissonance – Festinger
3. Robber’s cave – Sherif
4. Stanford prison experiment – Zimbardo
5. Obedience to authority – Milgram
6. False consensus bias – Ross
7. Social identity theory – Tajfel
8. Bargaining – Deustch and Krauss
9. Bystander apathy – Darley & Latane
10. Conforming to the norm – Asch

The imperfection of memory
My own favourite – the police lineup

The nightmare of miscarriage of justice happens. Evidence: currently 206 people have been exonerated by the Innocence Project using DNA evidence. Incorrect identification via lineups often contributes to wrongful judgements. (Who knows how many guilty people escape justice because of lineup muddles.)

In the traditional ‘simultaneous’ lineup method the witness tries to identify the guilty party by looking for him or her in a row of people or agroup of photographs.

A newer method is the ‘sequential’ lineup where the witness sees one face at a time. The idea is that instead of comparing the people in the lineup to each other the witness compares each face to the remembered face.

Makes sense, right? Except it’s been shown to be worse than the traditional method! A comparative study has shown that when using the simultaneous method witnesses made correct decisions in 60 per cent of cases (compared with 45 per cent when the sequential method was used).

Not only that, witnesses using the sequential method made incorrect choices 9 per cent of the time compared with 3 percent in simultaneous lineups.  So the sequential method produces more wrong calls and more non-calls (and we know from the simultaneous method that a good proportion of the non-calls would have been good calls).

Otago study
A fascinating study is being conducted in New Zealand by Rachel Zajac. In a version of the simultaneous lineup, witnesses are presented with several photographs – one of which may be of the guilty party. But there’s one brilliant addition – a blank sillouette of a face with a superimposed question mark. In other words the witness is answering this question: ‘Was the person you saw one of these people or could it have been someone else – that person, perhaps?’

The psychological research behind this experiment comes from work with children whose false identifications decreased substantially when offered the question-marked sillouette.

Could it be that by actually ‘seeing’ the possibility of someone else enables the witness to make better a choice?

Remember, there are two numbers that need improving

~the rate of incorrect identifications needs to be lowered. (I can imagine that the Zajac method will help)
~the rate of non-choices being made needs to be lowered without increasing the rate of wong calls. (It is plausible that the Azajac method may exaccerbate the problem by making non-choice easier).

The mind, hey – what a rat’s nest!

4 thoughts on “Irrationality – the example of the police lineup

  1. this is good. thanks for directing me to these studies. i didn’t know most of them. i like milgram and the standford prison experiment most (doesn’t everyone?), but i have to say that the cognitive dissonance one is very interesting, too. and the one you mention, about the lineup.

    we are so very fragile.

  2. ama – you’re welcome. The one that still gets me is ‘bystander apathy.’ Do you know it? In 1964 Kitty Genovese was murdered over the course of an hour(!) observed by dozens of people(!), none of who intervened or called the police. Apparantly we are less likely to help when there are others around – presumably because we assume someone else will step in. Hopefully knowledge of this effect has actually changed it in some instances.

  3. i learned about this when i was young. it wasn’t about genovese but about a violent rape in a subway station in paris. same difference. i was shocked, then indignant, then it changed my life. but i think i always assumed that no one will step in and that it’s up to me. i remember breaking a fight between two boys who were much larger than i when i was in grade school, in the street. i just put my body in between. for better or worse, i don’t get at all surprised when people do not step in. i expect it.

    i should also like to propose that it’s not just the assumption that someone else will intervene that stops people. it’s also embarrassment. in a crisis, we find standing out and drawing attention to ourselves impossibly anxiety-making. that’s why we substitute for the real thing by watching endless hollywood movies that are based precisely on the paradigm of the lone hero.

  4. ama – I’m sure you’re right, there must be deeper reasons. It’s interesting that I stopped with a more rational one. Wanting to let people off the hook for this dreadful tendency, I shouldn’t wonder.

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