Persuading a Jury

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Pennington and Hastie (1998) Evidence Order

To investigate the effects of jurors confidence and the order of evidence on jurors verdicts using 130 paid students from Northwestern and Chicago Universities using a Laboratory condition.

Participants were allocated to one of four conditions: Prosecution items (guilty) in story order, Prosecution items (guilty) in witness order, Defence items (not guilty) in story order, Defence items (not guilty) in witness order. All Participants listened to a tape recording of the stimulus trial and then responded to questions. They were asked to either reach a guilty or non guilty verdict on a murder charge and they had to rate their confidence on a 5 point scale. In the story order, evidence was presented in its natural order. In the witness order, items were arranges in the order closest to the original trial. 

Results - 

  • The story order persuaded more jurors of Caldwell's guilt in the prosecution case. I
  • f the defence presented its evidence in witness order, even more jurors would find a guilty verdict. 
  • If the defence had the benifit of the story orderm the guilty verdict rate dropeed to 31%
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Pennington and Hastie (1998) Cont.

Evaluation - 

  • Controlled conditions - reliable
  • Lacks Ecological Validity - decisions have no consequences
  • Cannot generalise findings 
  • Large, reliable sample
  • Geographically specific

Debates -

  • Usefulness - Essential to ensure that courtroom procedures do not advantage either prosecution or defence.
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Cutler et al. (1989) Expert Witness

Investigating whether hearing about psychological research from an expert witness makes an eye witness account less accurate when juror's make a decision using 538 participants in a lab experiment using a mock robbery trial which was focussed in eye witness evidence.

There were two idependant variables

The Witness Identifying Conditions (WIC) = Either good (no disguise;hidden gun) or bad (robber disguised;handgun)

Witness Confidence = Either 100% or 80% confident their identification was right

Results -

  • Juror's verdict = When WIC was good, more guilty verdicts given = increased accuracy if expert gave a Qual testimony.
  • Juror Memory = 85% correctly remembered;so poor memory can't be blamed.
  • Juror Confidence = Good in WIC condition and stronger if witness was 100% confident and if EW was confident. e.g. If a robbery had taken place and robber had used a disguise and a weapon, WIC would be bad.
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Cutler et al. (1989) Cont.

Conclusion -

  • Expert testimony improved knowledge and reduced reliance on witness confidence
  • Where no expert witness testimony given witness confidence effected judgement

Evaluation -

  • Lacks Ecological Validity - decisions have no consequences
  • Cannot generalise findings 
  • Large, reliable sample
  • Geographically specific
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Pickel (1995) Inadmissible Evidence

To look at how the credibility of the witnesss affects the jurors ability to ignore inadmissable statements using a mock trial with 236 Bali State University Psychology students using independant measures design.

Participants listened to an audiotape of the trial and them completed a questionnaire asking them to make several decisions on the case. One was their verdict, the second was their estimate of the probable guilt of the defendant and the third was a rating on a 10-point scale of the extent to which knowledge of the prior conviction caused them to believe the defendant was guilty. Finally, they have a rating on the credibility of each witness. There was a control group who didn't see the critical evidence.

Results -

  • Mock jurors who heard the evidence ruled inadmissible and who recieved no explaination did ignore the evidence.
  • Those who were given an explaination were less likely to find the defendant guilty. 
  • No significant effect in anything else.
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Pickel (1995) Cont.

Evaluation - 

  • Lacks ecological validity 
  • No consequence to participants decisions 
  • Geographically specific

Debates -

  • Psychology as a science? - High control, statistical analysis, replicable, objective, falsifiable
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Castellow (1990) Defendant attractiveness

To test the hypothesis that an attractive defendant is less likely to be seen as guilty. Secondly, when the victim is attractive, the defendant is more likely to be found guilty. Finally, to look for any gender differences in jury verdicts depending on attractiveness through a mock trial using 71 male and 74 psychology students from East Carolina University.

Participants were told that they would be reading a sexual harassment case and had to give the guilty/not guilty verdict and rate the defendant on 11 bipolar scales e.g. dull-exciting, nervous-calm.

Results -

  • Physically attractive defendants and victims were rated positively on other personality variables.
  • When the defendant was attractive, guilty verdict were found 56% of the time
  • Whereas were found 76% of the time for an unattractive defendant. 
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Castellow (1990) Cont.

Evaluation - 

  • Elimination of researcher bias because of independant rating of photos

Debates - 

  • Social Determinism of attractiveness
  • Ethnocentrism - attractiveness varies with social ideals 
  • Essential in identifying factors that could bias a jury
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Penrod and Cutler (1995) Witness Confidence

To examine several factors, including confidence, that jurors might consider when evaluating eyewitness identification evidence using a mock trial scenario with eligible and experienced jurors

A videotaped trial of a robbery was presented in which eyewitness identification played a key role. The witness was either 80% or 100% confident that she had identified the robber. Nine other IVs were introduced.

Results -

  • Witness confidence is the only statistically significant effect of all the 10 IVs.
  • In a further nine studies, Cutler looked at the relation between confidence and accuracy: it has a weak correlation.
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Penrod and Cutler (1995) Cont.

Evaluation - 

  • By using eligible experienced jurors the reliability is increased

Debates - 

  • Social determinism 
  • Shows that it is important that jurors must examine all evidence and aren't swayed by witness confidence
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Ross et al. (1994) Protective Shields and Videotap

To find out if the use of protective shields and videotaped testimony increases the likelihood of a guilty verdict. To investigate the effect of protective devices on jury reaction to testimony - do they experience credibility inflation or deflation? 300 psychology students were used; 100 in each condition. The three conditions used were; child in full view, child behind a screen, child giving testimony via a videolink. They were conducted using a mock trial.

Participants watched a version of the case. The judge read a warning before the shield and videolink were used, telling the jury not to imply guilty by their use. After the case, which was about potential sexual abuse, the participants gave their verdicts and rated the child on the credibility of the story.

Results - 

  • The guilty verdicts were no different between the conditions.
  • However 20% more females than males (58.6% against 38.6%) found the defendant guilty.
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Ross et al. (1994) Cont.

Evaluation - 

  • Large sample 
  • Students so unrepresentative
  • Mock trail - low in ecological validity

Debates -

  • Useful to know courtroom behaviours cannot bias judicial process
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Hastie (1983) Stages in Decision Making

Orientation period

  • Relaxed and open discussion
  • Set the agenda
  • Raise questions and explore facts
  • Different opinions arise

Open confrontation

  • Fierce debate
  • Focus on detail
  • Explore different interpretations
  • Pressure on the minority to conform
  • Support for the group decision is established


  • Attempts to smooth over conflicts
  • Tension released through humour
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Hastie (1983) Cont.

Evaluation - 

  • Not used findings from research specifically studying the courtroom so unreliable.

Debates - 

  • Reductionist - ignores individual personality features which could impact decision making
  • Situational explanations
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Asch (1955) Majority Influence

To investigate the effects of conformity to a majority when the task is unambiguous, using 123 male undergraduated in America using a lab experiment.

Naive (real) participants in a room with confederates (stooges or insiders). They are asked to the question 'Which of the three lines, A, B or C mathces the stimulus line X?'. The confederates clearly choose the wrong line.

Results - 

  • Asch found that individuals conformed in one out of three (32%) occasions.
  • When one confederate disrupts the conformity this falls to 5%.
  • Another finding is that majorities bigger than three make very little difference to the conformity effect. 
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Asch (1955) Cont.

Discussion -

  • The conventional view to conformity says there are two reasons why we conform: the need to belong to a group and the need to be right. 

Evaluation - 

  • Lacks ecological validity 
  • Gender-bias 
  • Important data about explanations of behaviour

Debates -

  • Social determinism - Situational explanations of behaviour, resisting conformity indicates free will.
  • Has implications for education/training
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Nemeth and Wachtler (1974) Minority Influence

To investigate the influence of perceived autonomy (choosing where to sit at a table) and consistency on minority influence using a mock trial with a group of 5 participants (one confederate) of adult students.

Participants have to deliberate on the amount of compensation due for a victim of an injury. After hearing the facts they go to a room with a rectangular table. One seat is at the end, and the others down the side. In half the groups the confederate chooses to sit at the head of the table (perceived autonomy). In the other half they are told where to sit. During the discussion, the confederate consistently adopts a deviant position, suggesting a figure of $3000 in compensation instead of $10,000-$25,000 which was the majority view.

Results -

  • The confederate exerts influence when he consistent and when he perceived as autonomous because he has chosen his seat, whereas when seated by the experimenter he has little influence. 
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Nemeth and Wachtler (1974) Cont.

Discussion - 

  • This has interesting repercussions for the jury room where people sit around a long table.

Evaluation - 

  • Controls (blind to hypothesis, training confederate) allows for greater confidence in results
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