DNA evidence often overwhelms jurors to convict wrongly says research

By Dr. Ananya Mandal, MDMar 29 2010

According to new reports from The Australian Institute of Criminology Research jurors are often not confident enough in their knowledge of DNA based evidence and this may often go against the accused as they may return with the guilty verdict. This is known as “the white coat syndrome” meaning laymen are often overwhelmed by the presence of an expert and as jurors may place more importance to these DNA evidence than necessary.

Professor Jane Goodman-Delahunty from Charles Stuart University says "They tend to regard it as infallible and so once it comes in, the very fact that the judge has admitted the evidence is often construed as an indication that it must be reliable, and therefore they rely on it without questioning it very thoroughly." "The conviction rate is far higher than the scholars think it ought to be, if you look at the weight that the evidence might warrant."

She pointed out potentials for common errors in DNA evidence were often disregarded by jurors or they may be unaware of them. These may be laboratory errors and ''random match probabilities'' - the likelihood of a coincidental match between the crime scene sample and a person.

Professor Goodman-Delahunty studied around 400 people to find what their responses were to a DNA evidence in some mock trials for murder. It is from this study that she concluded the less people understood the technology the higher were conviction rates. Low understanding of the technology translated to 75% conviction rates versus 42% conviction with better knowledge.

After the initial study she went on to give them a 20 minute basic know-how on DNA evidence technology and reassessed them.

"As their knowledge increased - and we tested that with objective multiple choice questions before and after exposure to the tutorial - their trust and reliance on the DNA evidence decreased. And the conviction rate also decreased.”

"I think it is a confirmation of concerns that have been expressed for a long time by courts, law reform commissions and lawyers about the impact of DNA evidence, possibly exacerbated by the popularity of shows like CSI and so forth, where this sort of evidence is rarely presented as including any potential for error," she said.

The chief executive of the Law Institute of Victoria, Michael Brett-Young, said,

"I think what we've got to understand is that DNA is not 100 per cent conclusive, and in that case we have got to use it as just one of the tools." "Juries should be instructed that they must make sure that they are 100 per cent and beyond reasonable doubt sure of guilt. One of the solutions is to make sure that the courts and in this case, judges, charge the jury and tell them that they must make sure that they are sure beyond reasonable doubt, and that it's not the only evidence they should use."

Professor Goodman-Delahunty said steps could be taken to stop this. "You could, for example, provide jurors-in-waiting with some background information in the form of a prerecorded, agreed-upon tutorial, where there's nothing controversial, and it's not about a specific case but just explains the procedure." “And then they would all be brought up to speed, so they're all on the level playing field as they go into the trial. Or you could include that sort of information in a presentation by the expert in the context of a case, which is how we tried it out in a trial simulation."