Comment »Posted on Saturday 24 April 2010 at 4:53 pm by Jacob Aron
In Getting It Wrong, Health & Medicine

Forensic experts are unable to accurately determine the age of bruises on the bodies of crime victims, say researchers at Queen Mary, University of London. A study published in the Journal of Forensic and Legal Medicine, suggests that sentencing of criminal cases involving bruising, such as child abuse or assault, could be based on flawed conclusions.

The researchers evaluated the bruise-judging abilities of 15 forensic experts with the aid of 11 willing volunteers and a suction pump. Each subject used the pump to inflict bruises on themselves, which the researchers photographed daily until they had faded completely. The photos were digitally altered to remove any hints that might aid the experts in estimating their age, such as marks from the suction pump, then randomly presented for them to judge. They were also asked to place a series of photos in chronological order, identifying how the bruise faded over time.

While we’re used to seeing experts on TV pin down the time of a crime to the nearest minute, the reality is somewhat different. The median difference between the expert’s assessment and the true age of a bruise was 26 hours, but some were even further out, with one expert getting it wrong by 454 hours or nearly 19 days.

Fresher bruises were easier to identify, with a 52% success rate for injuries under 12 hours old, but accuracy fell as the bruises faded. There was a slight increase in accuracy for injuries over 6 days old, but this could be due to chance as there were only a few bruises that lasted this long.

The experts fared better at the second task, placing the bruise images in chronological order without too many mistakes. The results seemed to depend on the nature of each bruise rather than the skill of the experts, because some bruises showed clearer changes in size and colouration than others.

Incorrectly judging the age of a bruise could have significant effects on a criminal trial, either by allowing perpetrators to get away with their crime or placing the blame on an innocent suspect. The study authors conclude that forensic experts’ estimates are unreliable at best, which calls into question whether they should be used in court at all.

Pilling, M., Vanezis, P., Perrett, D., & Johnston, A. (2010). Visual assessment of the timing of bruising by forensic experts Journal of Forensic and Legal Medicine, 17 (3), 143-149 DOI: 10.1016/j.jflm.2009.10.002

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