Forensic Psychology

OCR Forensic Psychology Studied


Ethical Issues

Ethics are a set of moral principles used to guide human behaviour. They are a means of determining what is considered right or wrong

5 key ethical issues in Psychology: 

  • Deception
  • Right to withdraw
  • Informed consent
  • Confidentiality 
  • Protection

Examples of unethical research: 

  • Asch, conformity study; deception and informed consent - told participants he was looking at perception when it was conformity, participants unaware there were confederates taking part in the study lying purposefully. Protection -  caused anxiety/people worrying they had poor eyesight, low self-esteem as easily influenced.
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Ethical Issues Continued; examples of unethical re

  • Moscovici, conformity study; deception and informed consent - participants unaware confederates taking part in the study and were purposefully lying, informed consent could not be gained as confederates used without participants knowing.
  • Milgram, obedience study; deception and informed consent - told the study was about bout memory and learning when it was about obedience, experimenter behavior and props such as generator, electrodes and "Mr Wallace" receiving the shocks seemed realistic but were fake. As participants were deceived they could not give informed consent. Protection - participants put under serious stress which led to extreme anxiety and distress. Right to withdraw - experimenter made it extremely difficult for them to leave and pressured them to stay and carry on. Milgram defended himself; informed consent would have left experiment pointless, participants were debriefed, had no idea the experiment would have the effect it did, only 1% of participants wished they hadn't been involved. 
  • Bandura, bobo doll study; right to withdraw - children do not understand it, protection - children conditioned to behave aggressively.
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Reaching a verdict; Persuading a Jury

Effect of order testimony

  • The way we receive information affects how we process and remember it. 
  • E.g. the primary effect - demonstrates that we are more likely to remember the first words in a list rather than ones in the middle or at the end. 
  • This might have a connection to our arousal level, its uniqueness, or how much effort we apply. 
  • Applied to the courtroom, although the defence closes last, this is followed by the judge summing up, this might wipe out any recency effect for the defence. 
  • Another important factor is how the counsel structured their cases; should they use story order - where the events unfold in chronological order? Or should they take advantage of primary and recency effects by using witness order - presenting their best witness first to last. even if this affects the order or events in the jurors mind?
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Reaching a verdict; Persuading a Jury

Effect of order testimony; key study: Pennington and Hastie - effects of memory structure on judgement.

Aims: To investigate whether or not story order evidence summaries are true causes of the final verdict and the extent to which story order effects confidence in those verdicts. 

Method: Lab Experiment 

Participants: 130 students, Northwestern and Chicago University, all paid, allocated to 1 of 4 conditions roughly equal in size.

Procedure: Listened to a tape recording of the stimulus trial > responded to written questions > asked to reach either guilty or not guilty verdict of murder > rate confidence in decision from 1 to 5 > didn't interact with each other >  in story order condition, evidence arranged in natural order > in witness order condition, evidence items arranged close as possible to original trial. 

Results: Greatest level in confidence of verdicts showed by those who heard defense/prosecution in story oder. Lowest confidence by those who heard witness order prosecution/defense. 

Conclusions: Presenting case in story order has persuasive effect > the effect in defense case much smaller, but probably because defense was much less plausible (victim fell on defendant's knife)

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Reaching a verdict; Persuading a Jury

The effect of expert witness on Jury Perception of eye-witness testimony

  • Expert witnesses widely used in criminal trials to add scientific confidence to evidence. From research by Loftus & Palmer we know that eye-witness testimony is extremely unreliable > Psychologists often called as experts witnesses for defence to warn jurors of possible problems with EWT. But research has shown that jurors tend to disregard these warnings and still believe in eye-witness accounts.

Key study; Cutler et al - The effect of expert witness on Jury Perception of eye-witness testimony. 

Aims: To investigate whether hearing about psychological research from an expert witness which casts doubt upon the accuracy of EWT would affect a juror's decision by making them more sceptical. 

Method: Lab experiment using a videotaped mock trial

Participants: 538 undergraduates; given extra credits for their introductory psychology course.

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Reaching a verdict; Persuading a Jury

Key study; Cutler et al - The effect of expert witness on Jury Perception of eye-witness testimony continued. 

Procedure: Viewed a videotaped mock trial of a robbery > individually completed a questionnaire containing the dependent measures which were verdict, a memory test and rating scales of how confident they were in their verdict. Four independent variables: 1. Witness Identifying Conditions (WIC) > Good (no disguise, 2 day delay in indentification, hidden gun, no suggestive instructions during line-up) or Bad ( disguise, handgun, 14 day delay, suggestive instruction during line-up) 2. Witness confidence; either 100% or 80 % confident of correct identification 3. Form of testimony > Expert witness either gave descriptive testimony or relied on figures and % 4. Expert opinion > expert gave opinion on scale of 1-25 on the accuracy of the testimony, this overlapped with the good/bad WIC in variable 1. 

Results: Juror's verdicts; when WIC was good, more guilty verdicts > effect increased if jurors given descriptive testimony. Juror's memory; 85% recalled the testimony, so poor memory cannot be blamed. Juror's confidence; higher in good WIC condition, stronger if had heard the expert witness and he was 100% confident (rather than 80%)

Conclusions: Expert testimony improves jurors' knowledge, made them pay more attention to witness identifying conditions, with expert testimony juror sensitivity to problems with evidence is improved and may help to prevent miscarriages of justice. 

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Reaching a verdict; Persuading a Jury

Effect of evidence being ruled inadmissible 

  • The law says in order for evidence to be ruled as inadmissible its relevance must outweigh its potential for discrimination.
  • Inadmissible evidence includes rumours, past convictions and evidence obtained by illegal means.
  • If inadmissible evidence is presented in error by a witness, the judge will direct the jury to disregard what they have just heard.
  • However, by drawing their attention to it, it may be that the jury in fact pays even more attention to it.

Key study: Pickel - investigating the effect of instructions to disregard inadmissible evidence. 

Aims: To look at the effect of prior convictions > to look at the role of judges instructions when they were followed by a legal explanation > to examine how much the credibility of the witness affects the juror's ability to ignore inadmissible statements. 

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Reaching a verdict; Persuading a Jury

Key study: Pickel - investigating the effect of instructions to disregard inadmissible evidence. 

Method: Experiment using mock trial using fictional theft with a mock jury > critical evidence introduced "accidentally" by witness > item objected to by attorney then either allowed or overruled by the judge > in one condition followed by legal explanation why the evidence was inadmissible > in second condition this explanation absent. 

Participants: 236 Psychology students, Bali State university, participated as course requirement, randomly assigned to one of the conditions, independent measures design.

Procedure: Listened to audiotape of trial > completed questionnaire making decisions about the verdict, probable guilt of defendant, 10 point scale on effect of knowledge of prior convictions, credibility or witness > control group did not get critical evidence. 

Results: Those who heard evidence ruled inadmissible but given no legal explanation likely to ignore it and find D guilty > those who heard evidence ruled inadmissible but given legal explanation less likely to ignore it and find D not guilty > no evidence found to suggest credibility of witness would affect juror's ability to disregard inadmissible evidence > no significant effect on use of prior conviction evidence as measured by the 10 point scale. 

Conclusions: calling attention to inadmissible evidence makes it more important to the jury.

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Reaching a verdict; Witness appeal

Attractiveness of the defendant 

  • "Halo effect" - when one favourable characteristic is known about an individual a positive halo of favourable characteristics is formed. 
  • When applied to the courtroom, a jury may make decisions about witnesses and defendants based on their physical appearance.

Key study: Castellow et al, The effect of physical attractiveness on Jury verdicts 

Aim: To test the hypothesis that attractive defendants are less likely to be seen as guilty. 

Method: Laboratory experiment using the mock trial format. independent measures design used. 

Participants: 71 males, 74 females, received extra credits for their psychology classes in East Carolina University. 

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Reaching a verdict; Witness appeal

Key study: Castellow et al, The effect of physical attractiveness on Jury verdicts 

Procedure: Participants told they would be reading a sexual harassment case and would have to answer questions on it > with the case there were attached photos of the victim and the defendant > these had previously been categorized as unattractive or attractive by a panel of 9 judges > dependent variable was measured by the answer to the question "do you think Mr Radford is guilty of sexual harassment?" > towards the end of the case booklet they were given, the participants had to rate the defendant and the victim on 11 bipolar scales e.g. dull-exciting.


  • Physically attractive defendants and victims were rated positively on other personality variables as well. 
  • Attractive defendant; guilty 56% of the time 
  • Unattractive defendant; guilty 76% of the time
  • No significant gender differences 

Conclusion: Although the findings come from a mock trial, when applied to a courtroom it seems that appearance does indeed have powerful effects on verdicts. 

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Reaching a verdict; Witness Appeal

Attractiveness of the defendant 

  • One of the most convincing features of a witness is their confidence when giving testimony. 
  • When a witness is confident the jury are convinced that the statements are more accurate. 

Key study: Penrod and Cutler - The effect of witness confidence on Juror's assessment of eyewitness evidence. 

Aim: To examine several factors, including confidence, which jurors may consider when evaluating eyewitness identification service. 

Method: Experiment using mock trial scenario, independent measures design. 

Participants: Undergraduates and eligible and experienced jurors. 

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Reaching a verdict; Witness Appeal

Key study: Penrod and Cutler - The effect of witness confidence on Juror's assessment of eyewitness evidence. 


  • videotaped trial of a robbery presented
  • the witness testified that they were either 80% or 100% confident in identification of the robber. 
  • Nine other variables, both high and low, were introduced into the film. 
  • Participants experienced either the high or low level condition variables on a random basis. 
  • After the film asked to state whether they though the robber was guilty or not guilty. 

Results: Witness confidence is the only statistically significant effect of these listed variables under the conditions of the mock trial. 

Conclusion: Confidence is a poor predictor of witness accuracy, jurors trust in confidence is undiminished. 

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Reaching a verdict; Witness appeal

Effects of shields and videotape on children giving evidence

  • In many cases the child is the only witness and giving evidence in court can be very traumatic for them. 
  • Children are therefore able to give evidence from behind a screen or from outside the courtroom e.g. via video link. 
  • having a child giving evidence behind a screen may suggest an increased likelihood of guilt to a jury by implication that the child needs protecting from the defendant. 

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Reaching a verdict; Witness appeal


key study: Ross et al - The impact on protective shields and videotape testimony on conviction rates

Aim: To find out if the use of protective shields and videotape testimony increases the likelihood of a guilty verdict > to investigate the effects of protective devices on jury reaction to testimony. Do they experience 1. credibility inflation; testimony enhanced because child protected from negative effects of trauma or 2. credibility deflation; where child witness seen as fragile and unreliable because of use of a shield.

Method: Mock trial based on real court transcript > professional film crew record actors playing roles > 3 versions: open court with child in full view, child behind a 4 x 6 ft screen, child testifies via video link. 

Participants: 300 college students, 100 in each condition, majority white middle class, introductory psychology class. 

Procedure: watched 1 of the 3 versions of 2 hr court case of alleged father-child abuse > abuse single touch while father giving child a bath > judge in case read warning that use of screen did not imply guilt > participants gave verdict and rated the credibility of child on various aspects of story > rated defendant on various aspects of credibilty.

Results: Guilty verdicts show no significant difference between conditions > 56% females and 38% males found D guilty > jury perception of credibility of D did not differ across conditions, females found D less credible > so the defendant is not more at risk of being found guilty if protective shields are used. 

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Reaching a verdict; Stages in decision making

Key study: Hastie et al - stages and influences on decision making

Hastie suggested that the jury goes through the following stages: 

  • 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
  • Reconciliation: Attempts to smooth over conflicts > Tension released through humour. 

Absorb information from the witness, counsel, judge and defendant > make sense of it all > select evidence > evaluate for implications > evaluate for credibility > construct a sequence on events > argue a case to achieve a verdict. 


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Reaching a verdict; Stages in decision making

Key study: Hastie et al - stages and influences on decision making

  • Hastie et al are applying findings from social-psychological research of group dynamics to the jury. 
  • the problem is that real juries cannot be studied for legal reasons so it is only an assumption that these processes occur. 
  • It needs to be questioned that the special circumstance of being locked in a room until you come to a unanimous decision means that this research needs to be applied with a degree of caution
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Reaching a verdict; Stages in decision making

Asch - Majority influence - an insight into the power of majority influence and conformity 

Aim: To investigate the effects of conformity to a majority where the task is ambiguous

Method: Lab experiment 

Procedure: Asch arranged for a naive participant to be asked a question to which several stooges of the experimenter had already clearly given a wrong answer > the confederates were told to give the same incorrect answer on 12 critical trials > In total there were 18 trials with each participant > In the first two trials confederates answered correctly > In 12 critical trials the confederates gave the wrong answers > 4 more where confederates gave the right answers.

Standard line      A     B     C 


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Reaching a verdict; Stages in decision making

He wanted to see that if even in a crystal-clear decision, an individual would defer to the majority. 

Results: Asch found that individuals conformed in 1 out of 3 occasions > 32% conformity rate > majorities bigger than 3 make very little difference to conformity rates > this may be because 3 is enough to create a group norm whereas 2 would be insufficient. 

Conclusions: Shows a surprisingly strong tendency to conform to group pressure > however, the majority does not have the same impact on each individual > Asch also saw that on two thirds of his trials his participants had remained independent as clear evidence of how

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Thanks alot for this

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