Associate Professor Kypros Kypri and his team published the results of their study today in the international scientific journal, Addiction.

Dr Kypri said the study found the number of assaults in the central business district fell from 33 a month before the restrictions were put in place in March 2008, to 22 a month afterwards.

Dr Kypri said the study compared Newcastle CBD assault rates with those in Hamilton, which operated without late-night trading restrictions until November 2009.

"Analysing the figures, statistically, to take into account a gradual long-term increase in assault rates in both places gives a relative reduction in late-night CBD assaults of 37 per cent," Dr Kypri said.

He said "the intervention appears to have reduced assaults after 3am by a 'dramatic' two-thirds", while assaults between 10pm and 3am fell by 26 per cent.

Dr Kypri said critics of restrictions often argued that cutting opening hours in one place simply shifted the problem to another.

"We tested this displacement hypothesis and found no such effect," Dr Kypri said.

"Further, we found evidence of reduced assaults before the 3.30am closing as well."

Dr Kypri said high rates of alcohol-related violence and social disorder had led authorities to impose restrictions on 14 Newcastle venues from March 2008.

The affected pubs and clubs were forced to shut at 3am - relaxed to 3.30am in July 2008 - with a lockout from 1.30am to stop patrons from moving between venues.

"Governments throughout Australia have so far resisted introducing earlier closing times," Dr Kypri said.

"One has to wonder what sort of reduction in harm would occur if licensed premises across Australia were to cease serving alcohol at 2am, as is required, for instance, everywhere in California, and how many serious injuries could be prevented."