by Diane Boudreau

Homicide detective Jim Brass rummages through a pile of pill bottles and drug paraphernalia on top of an expensive dresser. The owner of the dresser—Las Vegas casino mogul Tony Braun—lies dead in his living room down the hall. Brass is in the bedroom looking for clues about Braun’s suspicious overdose.

Using a pair of forceps, Brass lifts an empty balloon from the dresser and brings it to forensic scientist Warrick Brown, who identifies the residue inside as black tar heroin.

“Can you get a print off these balloons?” Brass asks.

Warrick gives Brass a condescending look.

“I can get a print off the air,” he says.

It’s a typical exchange on CBS’s hit television series CSI: Crime Scene Investigation. By the end of the show, a set of fingerprints—from Braun’s doggie door, not the balloons—leads the investigators right to the killers.

The heroes of CSI are forensic scientists. Not the police officers, private investigators, and lawyers featured on many TV crime shows. Each week, the scientists solve murders, rapes, and other crimes. They use fingerprints, DNA samples, clothing fibers, and even molecules of perfume. On the show, all of these pieces of evidence are shown as exceptionally accurate and reliable.

Reality, however, is quite different. The reliability of different kinds of forensic evidence varies widely, and the margin of error for many techniques remains unknown due to lack of research. Forensic scientists on CSI race back to the lab to run tests the same day the evidence is collected. In reality, the backlog for such tests can be months, if not years.

Of course, no TV viewers would believe that a fictional television show was completely accurate—would they? In the case of CSI, some people think they might.

The show premiered in 2000. A short time later, legal professionals began talking about what they perceived as a “CSI effect” on juries. The mass media latched onto the concept with a flurry of articles suggesting that the show affects jury decisions in courtrooms across the country. Oddly, the claims about how juries are affected contradict each other.

“Usually they were claiming that juries won’t convict, that they want DNA evidence for every trial. They are disappointed when they don’t get that. In that case you’d expect CSI to help the defense,” says Nick Schweitzer, a doctoral student in psychology at Arizona State University. “Some say that people are so enamored by the glamour of scientific evidence that they think it’s foolproof. This favors the prosecution.”

The articles are full of anecdotes from lawyers talking about cases where the CSI effect supposedly influenced juries. What they lack, however, is real data.

“I thought, ‘It seems like someone should do a study,’” says Schweitzer. “For all the talk, no one has studied this. I felt it needed some empirical research.”

Studying jury behavior is tricky. You can’t do controlled experiments on juries looking at real cases. Instead, Schweitzer used a transcript of a mock criminal trial. The main piece of evidence was some hair recovered from the crime scene. In the trial, a forensic scientist testified that he had analyzed the hair under a microscope and, in his opinion, the hair originated from the defendant.

Schweitzer presented the mock trial to 48 jury-eligible university students. He asked them to fill out a questionnaire about their perceptions of the trial as a whole and the forensic evidence in particular. He also questioned them about how often they watched forensic-themed crime shows such as CSI, and general crime shows like Law and Order.

Schweitzer is working with Michael Saks, an ASU professor of law and psychology, Schweitzer found that respondents who watched CSI-type shows were more skeptical of the forensic hair analysis than those who didn’t. They also claimed a greater understanding of forensic science and greater confidence in their verdicts.

But they weren’t more or less likely to convict.

“We didn’t find a significant effect on verdicts,” says Schweitzer. “The actual numbers were different—29 percent versus 18 percent [voting guilty]—but it wasn’t statistically significant.”

Schweitzer and Saks’ study appeared in the Spring 2007 issue of the law and science journal Jurimetrics. While the ASU researchers were conducting their study, some other researchers decided to tackle the subject as well, using a variety of methods including the mock trial.

The verdict on CSI? Not guilty.

“Not one single study shows a tendency to acquit based on CSI,” says Saks. “The study that Nick and I did is the first to suggest it might change how jurors look at cases. Our participants gave the forensic scientists a lower rating, but didn’t change their verdicts.”

Schweitzer notes that his study used a small sample size and was limited to college students. Perhaps jurors in a different age group or with different education levels would be more or less likely to acquit based on the forensic evidence. However, to date there is no real evidence that shows like CSI have an effect on trial verdicts.

“It could turn out that the CSI effect is urban legend,” says Saks.

Whether or not the CSI effect is real, many lawyers are treating it as fact. In Arizona in 2005, the Maricopa County Attorney’s Office conducted a survey of 102 prosecutors. The vast majority said they changed the way they prepare arguments and evidence in order to counteract an expected CSI effect among juries. They say they submit evidence for fingerprint and DNA testing even when it isn’t necessary, and try to inform jurors about the nature of such evidence during jury selection procedures.

The MCAO study is often cited as evidence supporting the existence of a CSI effect. Half of the prosecutors said that they had seen between one and five acquittals where forensic evidence was not presented, but they felt sufficient non-forensic evidence existed to prove guilt. One-third of them felt that more than five faulty “not guilty” verdicts had been reached.

However, the study didn’t measure the jurors’ actual reasons for acquitting or their television-viewing habits, only the prosecutors’ speculations. In fact, a comparison of trials across the United States. from before and after CSI came on the air shows that there has been no change in acquittal rates. Jurors are no more likely to acquit in the age of CSI than they were before it existed.

This doesn’t mean that the show has no effect on juror perceptions.

“People who watched were more skeptical of forensic science. They think they know a lot about it,” says Schweitzer. But he cautions that this doesn’t prove that CSI causes that mindset. “It may be that people who like these programs already have a different view of forensic science, which is why they are drawn to the program.”

Perhaps concerns about CSI’s effects are rooted in an overall uncertainty about how to handle new technologies and scientific evidence in the courtroom. Historically, the standard for allowing evidence into the courtroom was whether it was “generally accepted” as valid. Handwriting analysis is a good example. It is used in courts because people generally consider it a reasonable form of evidence. But that doesn’t mean it’s actually reliable.

About 15 years ago the standard for admitting evidence changed. Today, before allowing scientific evidence in a court, judges are supposed to evaluate if it is good science or not.

“This required judges to be more active gatekeepers, which of course has its own problems,” says Schweitzer. “They’re lawyers, not scientists. And they don’t always take their gatekeeping very seriously.”

They need to, however. Studies have shown that people are more willing to accept science that is presented in a courtroom than science that is presented in other places, such as the mass media. The trial context lends credibility to the evidence.

In his dissertation work, Schweitzer will examine how jurors understand scientific evidence—specifically, a research study. He will also test a 20 to 30-minute introduction to causality to see if it helps jurors better understand the study.

There are other ways to improve the use of science in court, as well. For very complicated cases, courts sometimes bring in special juries that have higher-than-average education levels or expertise on the field in question. Sometimes a court-appointed expert interprets the evidence for the jurors. The American Association for the Advancement of Science also offers a service to help judges locate neutral scientific experts to testify in trials, and to advise them on managing cases that use such experts.

“I’m certainly in favor of courts doing that more. Judges really need to be doing their jobs, because juries assume that they have screened the evidence,” says Schweitzer.

Where does this leave shows like CSI?

“It’s a perfectly fine show,” says Schweitzer. “If it was realistic it wouldn’t be that interesting.”

Like all works of fiction, CSI relies on a suspension of disbelief. And like all hot TV shows, it will eventually lose its popularity and be replaced by something else. But the use of complex scientific evidence is here to stay.

“This is kind of a demonstration of how media and fiction can affect jurors and trials,” says Schweitzer. “It is one factor in how jurors understand scientific evidence. My goal is to improve the quality of science allowed in courts and to improve jurors’ ability to understand it.”

For more information, contact Nicholas Schweitzer, Department of Psychology, 480.965.5766, njs@asu.edu; or Michael Saks, Sandra Day O’Connor College of Law/Department of Psychology, 480.727.7193, michael.saks@asu.edu