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Severity of traffic crash injuries commonly misclassified

St Clair Beach

Monday 31 August 2009 9:05am

New Zealand's current way of counting injury severity in people hospitalised from traffic crashes has serious flaws and could be replaced by a method yielding more accurate information, according to University of Otago research being presented today.

Study co-investigator Dr Gabrielle McDonald says that after assessing the validity of thousands of injury severity reports recorded over a five-year period, significant disagreement was found between the severity of people's injuries as officially recorded at crash sites and that shown by their subsequent hospital discharge data.

"One of our findings was that 15 per cent of those whose injuries were recorded as minor actually had injuries that posed a significant threat to life," says Dr McDonald, who undertook the research as part of her Master of Public Health studies through the University's Injury Prevention Research Unit.

Among other findings was that pedestrians were 1.6 times more likely to have a severe injury overlooked than crash victims in passenger vehicles, she says.

Under the current system, police attending a crash fill out a traffic crash report which codes injuries as "serious", "minor" or "fatal". The data is sent to the New Zealand Transport Agency, entered into a crash analysis system and used in road safety statistics.

After linking 14,869 cases of non-fatal injuries recorded in police crash reports between 2000 and 2004 with hospital discharge data over the same period, Dr McDonald and colleagues assigned a severity score to each case, using ICISS, an international classification system that calculates threat to life.

The researchers found that overestimating, as well as underestimating, of severity was common. Of the crash reports recording 'serious' injury, only 48 per cent were also judged serious by ICISS standards, she says.

Dr McDonald says there are several likely reasons why police crash reports do not agree very well with hospital discharge data.

"One is that the definition of serious injury in police crash reports includes broad diagnoses such as 'fracture'. This means, for example, a broken arm will be put in the same category as a broken back."

"As well as problems with definitions, the system also asks busy police officers, who are not medical professionals, to make accurate on-the-spot assessments of injury severity. Often, injuries may not be immediately apparent - especially internal ones - or may appear to be less or more serious than they really are."

Replacing the police crash report system with an objective one based on the analysis of hospital discharge codes and ICISS would greatly improve the reliability of New Zealand's road injury statistics, she says.

"The beauty of using discharge data is that it is based on information from health professionals and comes at the end of a hospital visit, by which time a clearer picture of injury severity has emerged."

Another advantage is that it would also capture injury information from traffic crashes that the police were not called to, she says.

Improved information would ensure that the effectiveness of New Zealand's road safety programmes could be more accurately evaluated and funding targeted towards problem areas that may currently be being overlooked, she says.

Dr McDonald is presenting the findings during the 18th Australasian Epidemiological Association Annual Scientific Meeting in Dunedin today.

The research was supported by a grant from the Road Safety Trust.

For more information, contact

Dr Gabrielle McDonald
Department of Women's and Children's Health
University of Otago

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