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Inside the Juror (Hastie, 1993, 1994)

The Psychology of Juror Decision Making

Edited by Reid Hastie

"Modern behavioral science has produced four basic models of juror decision making based on probability theory, "cognitive" algebra, stochastic processes, and information processing theory."

"The ultimate impact of any piece of evidence will vary depending on the context of other relevant evidence that is available."

JLJ - Let's see how the legal system views judgment and decision making through the eyes of a jury. Since jurors are selected randomly, lawyers have to find the right questions to determine if a potential juror is biased for or against their client.

IMHO, cognition is complex and cannot easily be reduced to a simplified model, no matter how hard you try. We all have complex ways to go about resolving disputes in our own world, and take these processes - whatever they are - with us into the jury box and into the deliberation room, when we are called on to serve as a juror.

I would also assume that a typical juror is persuadable by his/her peers - the strength of a lawyer's argument is one thing, and that of someone sitting next to you in the deliberation room another.

By adulthood we are all (or have become) experienced to some degree at reconstructing events which we did not witness, from the stories told and the available facts. We have all read the news stories of the accused and examined the presented facts which point to guilt, or not. Sometimes there are reasonable explanations for what otherwise would appear to be involvement in illegal or unwise activity.

Human beings are essentially story-telling animals. A juror simply hears the presented facts (that the judge and the rules of law allow to be presented) and listens to the interpreted stories presented by counsel of both sides. One simply determines the facts and weighs the stories - and chooses one to believe over the other, much as one chooses one apple over another in the produce section of a grocery store.

p.3 Each of the major chapters in the present collection proposes a model of juror decision making... At present, none of the models is preeminently successful; we are at an early stage in the science of juror decision making.

p.5-6 The research in the present volume focuses on the manner in which jurors behave before they enter the social context of deliberation in criminal felony cases. Most jurors seem to have reached an initial decision about the appropriate verdict in a typical criminal trial, before entering deliberation

p.10-11 Modern behavioral science has produced four basic models of juror decision making based on probability theory, "cognitive" algebra, stochastic processes, and information processing theory.

Some steps between attitudes and verdicts, Phoebe C. Ellsworth, p.42-64

p.42 In most cases the weight of the evidence is insufficient to produce first-ballot unanimity in the jury... Different jurors draw different conclusions about the right verdict on the basis of exactly the same evidence... first ballot splits are the best-known predictor of the final jury verdict.

Algebraic models of juror decision processes, Reid Hastie, p.84-115

p.84 The use of algebraic equations to describe mental processes has been common in psychology since the field became an empirical science.

p.85 It is important to recognize the significance of the acceptance of a quantitative representation of the "meaning" of information such as the evidence presented at trial. Once we shift to numbers, we have implicitly conceded that operations on numbers are admissible models of mental processes.

p.85 After the information has been converted into numbers, usually ranging from 0 (implies innocent) to 100 (implies guilty), the decision maker's thinking process is represented by algebraic calculations... the equation used to combine the values is not consistent with standard probability theories. Rather, each number representing a piece of information is weighted according to its perceived importance and relevance to the ultimate judgment and then all the weighted numbers are summed to yield a global average evidence value.

p.85 Actually two general types of algebraic information combination processes have been proposed in applications to jurors' decision making. The first represents the process by which the evidence is combined as a one-step calculation in which all of the sources of evidence are evaluated (on the innocent-guilty continuum) and then one global weighting and adding calculation is performed.

The second "sequential" algebraic model also supposes that the basic judgment process is a matter of weighting and adding the values of pieces of evidence. However, the sequential model assumes that the process operates repeatedly, calculating a current average value by weighting the past opinion (based on evidence received up to that point in time) and calculates a new opinion according to the perceived strength of implication of the most recent piece of evidence and the importance (weight) of the new information. The basic image of the sequential decision process is of movement of a frequently updated current opinion along a unitary innocent-guilty belief continuum.

p.86 Theorists applying the algebraic modeling approach conceptualize the task of the juror as involving the integration of conflicting information from several sources into a decision to convict or acquit the defendant in a criminal trial. The juror arrives at a degree of belief that the defendant is guilty based on the implications of relevant information and this belief is then compared with a decision criterion value representing an interpretation of the standard of proof (usually "beyond reasonable doubt"). If the strength of belief in the defendant's guilt is greater than the criterion, the the decision is to convict.

p.87 The ultimate impact of any piece of evidence will vary depending on the context of other relevant evidence that is available.

p.89 The averaging model predicts that the scale values of evidence items will combine linearly under the assumption that weights are constant over stimulus manipulations; that is, the scale values for information items are independent and should show no interaction in different combinations.

[JLJ - Yes, but we seem to be missing a big thing here. In order for a Juror to assemble evidence in such a fashion, are we not implying that the "picture" painted by the evidence is murky, unclear, conflicting. It is pointless to ponder in such a fashion if there is a "home run" piece of evidence such as a "dash cam" video of a car accident, or a keenly observant witness standing nearby with an attentive clear view of what happened. If the defense attorney can convince the Jurors that one piece of evidence trumps all others (consider from the O.J. Simpson murder trial, the famous "if the glove don't fit you must acquit"). In this case, the other evidence, whatever it is and whatever it might imply, might simply be dismissed. I would argue that Jurors use the presented evidence to construct a story of what happened that they believe. They base their convictions of guilt or innocence on such a constructed story as a substitute and replacement for actual real events - the evidence items presented compete with each other for inclusion in (or dismissal from) such a constructed story.]

p.109 Another problem with the sequential averaging model is that it does not appear to precisely fit the quantitative data from mock-juror judgments.