A 27-fold increase in the number of narrative verdicts issued by coroners may be masking the effects of the current economic crisis on suicide rates, doctors have warned.
Professor David Gunnell, of the University of Bristol, said there is a "new and growing problem with the accuracy of national data".
Changes are urgently needed to ensure the future reliability of statistics and figures for the years "when narrative verdicts proliferated should be treated with caution", he said.
More than 3,000 narrative verdicts were recorded by coroners in 2009, compared with just 111 in 2001, figures showed.
While narrative verdicts can give more details about a death and help identify inadequacies in systems and procedures, they replace the short-form verdict of suicide, making it harder to classify some deaths as suicide and leading to some being recorded as accidents instead.
He called for all narrative verdicts to be accompanied by a short-form verdict in future, making it easier for officials to classify the deaths.
Suicide accounted for 4,648 deaths in England and Wales in 2009, figures showed, but the figures may be underestimating the scale of the problem, he said.
Estimates by the Office for National Statistics (ONS) showed that if all deaths from hanging and poisoning which were given narrative verdicts by coroners and coded as accidents by the ONS were suicides, the 2009 suicide rate would have been underestimated by up to 6%.
An ONS spokesman said: "ONS is confident that the overall picture of current suicide trends shown by National Statistics is reliable, but the variation in practice by different coroners means that local figures could be less reliable.
"We are working with coroners, and others concerned, to resolve these issues."
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