Murder rates would be up to five times higher than they are but for medical developments over the past 40 years.

According to new research, doctors are saving the lives of thousands of victims of attack who four decades ago would have died and become murder statistics.

Although the study is based on US data, the researchers say the principle applies to other countries too: “There is reason to expect a similar trend overall in Britain,” said Dr Anthony Harris, the lead author of the study.

In the research he and a team from Massachusetts University and Harvard Medical School found that technological developments had helped to significantly depress today's murder rates, converting homicides into aggravated assaults.

“Without this technology, we estimate there would be no less than 50 000 and as many as 115000 homicides annually instead of an actual 15 000 to 20000,” they say in a report of the study in the journal Homicide Studies (2002;6:128-66).

The team looked at data going back to 1960 on murder, manslaughter, assault, and other crimes. It merged these data with health statistics and information on county level medical resources and facilities, including trauma centres, population, and geographic size. The researchers then worked out a lethality score based on the ratio of murders to murders and aggravated assaults.

They found that while the murder rate had changed little from a 1931 baseline figure, assaults had increased. The aggravated assault rate was, by 1997, almost 750% higher than the baseline figure.

The team also described the dramatic overall decrease in trauma mortality in the second half of the 20th century.

The period of greatest change came between 1972 and 1977, on the heels of the US involvement in the Vietnam war, which triggered big advances in trauma care.

The team found that at county level significant drops in lethality of assault were linked to availability of high levels of care. The impact of a county simply having a hospital also had a significant impact, reducing lethality ratios by as much as 24% a year.

The researchers also highlight an irony in the life saving achievements of medical technology and doctors. Keeping down the murder rate may, perversely, have influenced the debate on gun control.

“Our lethality findings are strongly consistent with the hypothesis that progress in emergency medical care has converted an ever increasing proportion of homicides into non-lethal assaults and thus, by virtue of good intentions, ironically and unintentionally masked a continuing epidemic of violence in America,” says the report.

“Clearly, there is less perceived need to find common cause on gun control if the perception is that severely wounded victims of knives and automatics are routinely ‘repaired’ and back on the streets in no time.”