Persuading a jury

Pennington and Hastie



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  • Created by: Amy Leech
  • Created on: 28-03-13 12:30

Pennington and Hastie; Effects of evidence order o

Background: Previous research on primacy and recency effects cannot be applied to the courtroom and to the possible advantage/disadvantage to defence/prosecution because of concflicting findings.

Aim:To investigate the effect of story order and juror's confidence on juro's verdicts.

Sample: 130 Paid students at Northwestern and Chicago Universities, USA.

Method: Lab experiement with independant measures design. Participants allocated roughly equally to one of the four conditions: hearing 39 prosecution items (i.e. 'guilty' evidence) in 1. stroy order or 2. witness order; hearing 39 defence items (i.e. 'not guilty' evidence) in 3. story order or 4. witness order. Participants first listened to a tape recording of a stimulus trial (which had been edited/adapted from a real-life case to follow evidence items according to condition assigned), then responded to a questionnaire whee they were asked to give a verdict (guily/not guilty) and rate confidence in their decision on a 5 point scale.

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Pennington and Hastie; Effects of evidence order o

Results: Story order resulted in 59% guilty verdicts compared to 31% in witness order (for prosecution items) and a 78% guilty verdicts compared to 63% in witness order (for defence items). Greatest confidence was expressed by those who heard evidence in story order (either defence or prosecution).

Evaluation: Conmtrolled for primacy and recency effects, therefore reliable and higher confidence in results. Its essential to ensure that courtroom procedures do not advantage / disadvantage either prosecution or defence counsel and thereby pervert the course of justice.

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Cutler; The effects of expert witness testimony on

Background: There is a concern from previous research about jurors' over-reliance on eyewitness testimony, which calls into question their scrutiny of evidence.

Aim: To investigate the effects of expert testimony (which casts doubt on the accuracy of eyewitness testimony) on juror's judgements.

Sample: 538 introductory psychology undergraduates, given extra course credits, USA.

Method: A lab experiment. A videotape of a mock, armed-robbery trial (following format of actual trial) was viewed by participants in small groups (2-8 participants), who then independently completed a questionnaire on dependent measures, memory test and rating scales. IVs: 1. Witness identifying conditions (WIC) either poor (robber disguised, brandishing handgun, 14 day delay in witness idenfication) or good (robber not disguised, handgun hidden, 2 day delay in witness identification). 2. Witness confidence either high (testified 100% confident in correct identification) or law (testified 80% confident). 3. Expert witness (psychologist) testimony: either descriptive only or descriptive and quantified (or no expert witness). 4. Expert witness opinion on accuracy of identification (rating scale, 0-25, where 0= least likely to be correct): either low (7 in poor WIC trials), or high (20 in good WIC trials), o rno expert witness. DVs: 1. verdicts (guily/not guilty); 2. Memory test; 3. Juror knowledge; 4. rating on probability that a) D guily; b) eye witness identification correct.

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Cutler; The effects of expert witness testimony on

Result: When WIC good, higher percentage of guilty verdicts given, (effect increased where expert witness had given decriptive testimony). Jurors memory was tested to rule out poor memory as a possible confounding vaiable (85% correctly recalled testimony). Ratings of credibility of witness varied with witness confidence levels: witness rated more credible when she testified 100% confident in identification. Jurors had greater confidence in the accuracy of the witness identification when WIC were good (with a stronger effect with witness testifying 100% confident). Correlation between verdict and jurors perceived probability that identification was correct = 0.66.

Evaluation: Expert testimony imporved jurors knowledge and in some form reduced jurors reliance on witness confidence (e.g. jurors paid more attention to evidence). Where no expert witness testimony was given, witness confidence effected jurors judgements.

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Pickel; The effects of inadmissible evidence on ju

Background: Judges may rule evidence/testimony as inadmissible if it is believed that jurors may be unduly influenced by it, but previous research has sometimes shown thaat instructions to disregard evidence makes it mroe salient (known as reactance theory).

Aim: To investigate whether evidence ruled inasmissible by a judge influences jurors verdicts, whether the credibility of a witness affects jurors ability to disregard inadmissible testimony from that witness and whether the 'fairness' of evidence influenced jurors verdicts.

Method: A series of experiements using independant measures designs, where participants were randomly allocated to conditions.

Experiment 1: Sample; 236 psychology students at Ball State Uni. Method;Prior conviction evidence (8 different versions of an audiotape). IVs 1. Evidence of prior conviction (four condition): a) admissible, b) inadmissible without explanation, c) inadmissible with explanation and d) control (critical evidence not presented). 2. Credibility of witness (two conditions): a) high credibility, b) low credibility. DVs: 1.verdicts (guilty/not guilty). 2. Estimate of probability of D's guilt. 3. Rating (10point scale) of extent to which evidence of prior conviction caused belief in D's guilt. 4. Rating (7point scale) on credibility of witness. Participants first listened to an audiotape of a fictional trial involving theft. Results: The higherst percentage of guilty verdicts were given in the evidence ruled admissible condition and the lowest given in control and inadmissible without explanation conditions, Significant credibility high (58%), compared to low (44%).

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Pickel; The effects of inadmissible evidence on ju

Experiment 2: Sample; 290 psychology students at Ball State Uni. Method; Hearsay evidence followed a method/procedure similar to Experiment 1 except hearsay evidence presented (where witness reported hearing someone else say the D had said something incriminating). Results: A higher percentage of guilt ratings was higher when witness credibility was high. 

Experiment 3: Sample: 121 psychology students at Ball State Uni. Method; Hypothesised that 'hearsay' would be considered less fair than prior conviction evidence. Results: The results supported the hypothesis: hearsay evidence received a lower fairness rating.

Evaluation: Mock trial evidence, mock jurors and lab settings all mean that the studies lack ecological validity; we don't know if jurors would make the same decisions in real life (here decisions have no consequences); cannot apply/generalise findings. Large reliable samples, but geographically specific and students are atypical/unrepresentative. Situational eplanation of behaviour/social determinism (courtroom procedures) are not very useful, but very useful to identifiy any courtroom procedures which could adversely affect the course of justice. Psychology as a science - high levels of control/standardisation, statistical analysis means research meets criteria for replicability, falsfiablity and objectivity.

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