LAST SPRING'S ACQUITTAL of four police officers accused of beating Los Angeleno Rodney King may have shocked a nation, but it demonstrated what psychologists have known all along. It's terribly difficult to predict jury behavior.
What juries do consider in reaching a verdict and what they are supposed to consider may be two entirely different things. Scientists, for example, are just beginning to understand how juries react to "extra-evidenciary information"-or what's not legal proof.
Despite a judge's instructions to the contrary, jurors are in reality influenced by:
• all testimony presented during a trial
• a witness's refusal to take the stand
• the lawyers' opening and closing statements
• a defendant's attractiveness and prior criminal record.
How jurors process what is admissable, reports psychologist Gary Wells, is less clear. His own work shows that evidence must have "a kind of flavor to it" to make an impact on a jury.
For example, jurors often refuse to base their verdict on numbers and probabilities presented during a trial-so-called naked evidence. The same numbers carry weight with jurors only when couched in a statement of opinion, says Wells, a professor at Iowa State University.
An expert who says "I strongly believe that there is a 99 percent probability that the semen is the defendent's" will sway the jury more effectively than the lawyer who says 'the probability the semen was the defendent's is 99 percent." It's the same "naked" evidence, but cloaked in more human format.
Juries will also fill in the gaps of witnesses' testimony with a story constructed from their own inferences, says Valerie Hans, Ph.D., a social psychologist at the University of Delaware.
During the Rodney King trial, for example, jurors who believed the officers were guilty might weave elements of racial bias into their story to construct a version of the truth they feel more comfortable with, Hans says.
Also, many jurors on their own consider the "contributory negligence" of a defendent, Hans points out. Jurors' post-trial comments about King's "control of the situation" suggest a willingness by some jurors to believe King could have avoided the violent attack.
Further, the trial's frame-by-frame videotape viewings had an effect of its own, Hans says: It desensitized viewers to the attack's violent overtones. And the change of venue from a diverse urban area to a homogeneous suburban community was also critical to determining the trial's outcome.
Hans and Wells both worry about a fair retrial after Los Angeles' riots, but both still believe in justice by peer review.
"These aren't weird juries-these are just people," Wells says. "They're taking it very seriously and they're trying to reach a verdict." Oyez! Oyez!