One popular topic among legal scholars is how jury makes their decisions. Numerous scentific models have been provided to simulate juror’s decision process. A commonly known scientific model is the Bayesian model based on the theory of probability. Under the Bayesian model, the jury decision process is presumed to be a rational process. The model starts by providing a priori probability of juror’s verdict based on previous probability distribution under the circumstances, and then, “update” the juror’s projections based on new information and jury instructions. But a fundamental flaw of the Bayesian method is that people do not always behave according to probability principles. Moreover, the cognition of the fact is usually not a rational judgment. More recent studies suggest that although the cognition process of a person can be categorized under the Bayesian model, this model needs to be adjusted based on the source of evidences and how the evidences are formalized. This adjustment leads to the popular use of the so called “story model” nowadays for characterizing the jury verdict process.
The theory that underlies the story model is cognitive psychology. Under the story model, the primary process performed by jurors is the formalization of the entire story. Studies have shown that when making decisions, jurors do not normally weigh each and every piece of evidence individually. Instead they typically form two competing stories and decide which one is more probable. More specificity, in their quest for facts that leads to the verdict, they typically go through three steps, which include (1) forming a story, (2) understanding the law, and (3) applying the law to the story. But in practice, step (1) is usually more heavily weighted as a juror’s primary responsibility, as compared to steps (2) and (3). Although a commonly known challenge of trial by jury is the jurors’ understanding of jury instruction and the relevant law. The process of jurors learning the law in order to correctly categorize the story under the applicable law is often treated lightly. This ability of categorizing the story is considered a skill that does not need special training, but derived from juror’s life and experience. To ensure the continuity of evidence presentation, the judge gives jury instructions only after all the evidences are sufficiently debated between the opposing counsels.
This process, although reasonable to some extent, can be problematic from the view of cognitive psychology. The processes of presenting evidence, cross-examinations, and court debates can last for days. It is almost impossible to ask the jurors not to make any inferences or connecting the dots of evidences before the jury instructions are given. When the jury instructions are provided, the jurors may have already formalized their version of the entire story. If the story is inherently inconsistent with the jury instruction, the substantive content of jury instructions is often ignored. Moreover, jurors may need to adjust their story to adapt to the instructions when their memory of the evidences is vague after a long trial, which makes it more challenging for them to apply the instructions against the fact they remember. To solve this problem, providing jury instructions prior to the trial may be considered. This may help guiding the jurors to focus on important and legally relevant evidences, rather than burden them with all the details that may complex rather then complement their decision process.