This is the last of eight blog posts written by undergraduates in PSY102: Introduction to Cognitive Psychology, Summer Term I 2019.
In the criminal justice system, one might imagine that the more serious a crime is, the more extensive the evidence should be to support the verdict. However, a recent study conducted at Duke University finds that jurors assessment of guilt is less reliant on the type of evidence and more on the severity of the crime.
Mock jurors in the study were more likely to find someone charged with murder guilty than someone charged with robbery.
Numerous scholars have looked at how flawed forensic evidence, mistaken eyewitness identifications and defendants’ prior criminal convictions can introduce errors in criminal prosecutions.
But John Pearson, an assistant professor in four Duke departments including neurobiology, and his colleagues in law wanted to know whether the type of crime can also lead to a greater chance of wrongful conviction. It may be that jurors use moral and emotional responses to various crimes as reasoning for the decisions they make regarding the defendant’s guilt.
The researchers aimed to understand the relationship between crime severity and confidence in guilt by seeing how mock jurors, practicing prosecutors, and other practicing lawyers weigh various types of evidence in order to make a decision on guilt.
Participants in the study were subjected to about 30 crime scenarios, each one paired with a random variety of types of evidence. After participants read through each respective scenario, they rated the strength of the case on a 0-100 scale and their emotional and moral responses.
It appeared that the more threat or outrage they felt toward crime type, the more likely they were to find the defendant guilty.
The authors also tested different types of evidence’s potential interaction with people’s beliefs.
They found that both DNA and non-DNA physical evidence had the highest amount of influence on participants, but the difference between how the participants weighed them was small. The jurors appeared to place very similar, if not the same amount of weight onto these two types of evidence in terms of their confidence.
Pearson refers to juror’s equal weight of DNA and non DNA evidence as the “CSI effect.” But DNA evidence is far more reliable than non DNA evidence. The CSI effect lays out that jurors tend to give more weight to conclusions based on traditional evidence. The study found that no matter one’s position, the pattern of similar weight between the DNA and non DNA evidence was found across all groups. The study also states that “subjects tend to overweight widely used types of forensic evidence, but give much less weight than expected to a defendant’s criminal history.”
Along with finding similar patterns between confidence in guilt and evidence type, researchers also discovered an intense link between the subject’s confidence in guilt with the severity of the crime.
Notably for jurors, crime type highly influenced their perception of confidence in guilt. The study showed a positive correlation between personal, emotional, and moral biases and “adjudicative bias,’ or the likelihood of conviction.
And while jurors did show more of a trend in this finding, practicing lawyers and prosecutors also exhibited a crime-type bias correlation with the seriousness of crime, even though it was much smaller.
The study’s results model how punishment, outrage, and threat are almost entirely dependent on crime effect and crime scenario. This indicates that despite how much evidence was presented, crime type alone influenced jurors decisions to charge someone as guilty of that crime more frequently.
This could mean that regardless of how much evidence or what type of evidence is present, innocent people wrongly charged of crimes could more easily be convicted if it is a more severe offense.
These findings indicate how easy it is to reach wrongful convictions of severe crimes within the US criminal justice system.
Guest post by Casey M. Chanler