Forensic psychology- reaching a verdict

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  • Created on: 16-12-13 19:18

Pennington & Hastie

Aim: To study the effects witness order or story order has on the veridct and the confidence of the verdict 

Sample: 130 students, northwestern and chicago university, paid, 

Procedure: listened to a tape recording, reached a verdict and then answered a questionaire, rated the confidence in their verdict on a scale of 1-5, they were not allowed to interact with one and other, Ps were arranged in 4 conditions 

  • 39 prosecution items in story order/ 39 defence items in story order
  • 39 prosecution items in witness order/ 39 defence items in witness order


  • when the prosecution present in story order more gulity verdicts given
  • when the defense present in witness order more guilty verdicts given
  • greatest confidence defence prosecution story order, least confidence when two story order conditions
  • the defence case was much less plausible (the victim was drunk and fell on the knife) 
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Aim: to investigate whether an expert witness affects the jurors decision 

Participants: 538 undergraduates, given extra credit 

Method: lab experiment, video taped mock trial of a robbery, completed a questionnaire on their verdict, memory, and confidence in verdict, there were 4 independent variables 

  • 1. witness identifying condition: good (no disguise, 2 day recall) bad (disguise 14 day recall) 
  • 2. witness confidence: 100% or 80% 
  • 3. form of testimony: expert gave descriptive testimony or relied on facts and figures
  • 4. expert opinion: expert expressed an opinion on a scale of 1-25 how confident they were


  • Jurors verdict: when WIC was good more guilty verdicts, even more when expert witness gave descriptive testimony 
  • Jurors memory: 85% correctly recalled the testimony 
  • Jurors confidence: higher in the good WIC condition, stronger (100% not 80%) if heard an expert witness. 
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  • to look at the effect of prior convictions,
  • the role the judges instructions play when followed by a legal explanation, 
  • examine how much the credability of witness affects the jury ability to ignore inadmissiable evidence 

Sample: 236 psych students, ball state university, course requirement to take part, 

Method: experiment using an audio taped mock robbery trial, critical evidence introduced 'accidentally by witness, in one condition judge explained while inadmissiable in other he didnt, then completed a quesitonnaire on the verdict, probable guilt of defendent, 10 point scale on effect of previous convictions and credability of witness


  • those with no explanation could ignore it and found defendent guilty 
  • those who had explanation couldnt ignore it, defendent not guilty. 
  • credability of witness had no effect on it 
  • significant effect on the use of prior convictions
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aim: to test the hyptothsis that attractive defendents are less likely to be seen as guilty 

Participants: 71 males, 74 females, recieved extra credit, east carolina university 

Method: Laboratory experiment using mock trial, independent measures, read a sexual harrasment case with attaced photos of victims/ defendents, been rated by a panel of nine judges, dependent variable was the question 'do you think Mr Radford is guilty of sexual harrasment?' , had to rate victim defendent on 11 bipolar sclaes e.g. dull exciting 


  • physicaly attractive defendents and victims were rated postively on scales 
  • attractive defendent, guilty = 56% of the time 
  • unattractive defendent, guilty 76% of the time 
  • no significant gender differences 
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Penrod & Cutler

Aim: to examine several factors including witness confidence, which jurors may consider when evaluating eyewitness indentification 

Participants: undergraduates, eligible and experienced jurors

Method: experiment using a videotaped mock robbery trial, independent measures, witness either testified they were 80% or 100% confident, nine other variable introduced e.g. suspect in disugise, weapon focus. participant experienced high or low conditions randomly, after film stated their verdict. 

Results: witness confidence only variable that had a significant effect,  100% confident= 67% convicted 80% confident= 60%

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Aim: to find out if the use of protective shields and videotaped testimony affects likelihood of a guilty verdict, whether jury experiences credability/inflation 

Participants: 300 college students, introductory psychology class, majority white m/c, 100 assigned to each condition

Method: participants watched 2 hour film of a court cast of alleged abuse agaisnt a child from her father, the abuse was a single touch in the bath, the judge said before each screen that their use should have nothing to do with the verdict, after trial Ps gave their verdict and rated credability of witness and defendent. 


  • no difference in verdict between conditions (slightly more conviciton in video testimony) 
  • 58.6% of females gave guilty verdict compared to 38.6% for men
  • credability was no different between conditions although, females said defendent less credible and child more credible
  • Ross went on to do further research where he stopped the trial after child testified, results showed a clear difference between conditions.  
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orientation period: 

  • relaxed and open discussion 
  • set the agenda 
  • raise questions & explore facts 
  • different opinions arise 

open confrontation: 

  • fierce debate 
  • focus on detail 
  • explore different interpreatations 
  • pressure on minority to conform 
  • support for group desicion established 


  • attempts to smooth over conflicts
  •  tension released through humour 

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Aim: To investigate the effects of majority influences 

Method: lab experiment, asch arranged for a naieve P to be asked a question to which several stooges gave the wrong answer, In total there were 18 trials, in the first 2 the confederates answered correctly, followd by 12 where they gave the wrong answer and another 4 with the right answers, the critical question was 'which of three lines ABC clearly matches stimulus line X?' 


  • individuals conformed in one out of three occasions (32% conformity rate) 
  • when one stooge doesnt conform, conformity rate drops to about 5% 
  • any majorities bigger than three make little difference to the conformity effect. 

3 reasons for this... 

  • distortion of perception- they really did think the stooges wrong answers were right 
  • distortion of judgement- they felt doubt about their judgement 
  • distortion of action- they didnt want to be ridiculed so went along with the group
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Nemeth and Wachtler

Aim: to investigate the influence of percieved autonomy and consistency on minority influence 

Participants: groups of five participants (one a stooge) drawn from an adult sample of students 

Method: Lab experiment, have to debate the amount of compensation due for a victim,

  • first everyone makes individual verdict, 
  • then taken to another room where there is rectangular table, 
  • in half of the groups stooge picks head of table, other half experimenter tells people where to sit, 
  • confederate adopts a deviant position suggesting figure of $3000 instead of $10,000


  • confederate exerts influence when he is autonomous (chose seat) 
  • when seated by experimenter little influence
  • mesured by the difference between original verdicts and later verdicts. 
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