The Sydney Morning Herald quoted him as saying many of the costs totalling $15b in that study were inadmissible in a standard economic framework.
"My worry has been that while the $15b is economically meaningless, it is policy meaningful," he said.
"If people expect this is a cost to their back pocket because of other people's behaviour, that increases the demand for certain types of policy."
During the briefing, he was questioned over his impartiality given that his research and visit was financed by the alcohol industry, the paper reported.
He responded by saying he was subject to his university's strict controls to ensure academic freedom.
A spokesman for the Distilled Spirits Industry Council of Australia said it had taken advantage of Dr Crampton's visit to Australia, to address a liquor stores conference on the Gold Coast, to invite him to the Canberra briefing.
Today, the University of Canterbury backed Dr Crampton.
"Eric maintains ownership of his report which lets him publish regardless of whether the sponsor is happy. I am fully confident that Eric's study on the subject is totally independent," the university's Economics and Finance head of department Bob Reed said.
"It must be noted that Eric had reached these conclusions about proper method long before working on this project. Eric, like all our researchers, is compliant with UC's research conduct."
Dr Crampton said an Australian alcohol consortium hired him through a grant administered by the university and subject to its research guidelines. He was asked to evaluate whether an Australian study on the social cost of alcohol followed normal economic method and disclosed the funding more than a year ago.
He cited the most current Ministry of Social Development social report which shows that problem drinking among 15-24 year olds - the narrowest category on which they reported - has not increased substantially since the lowering of the alcohol purchase age.
"Why should we expect that increasing the purchase age will reduce harms now when reducing the purchase age did not change the rate of potentially hazardous drinking?" he said.
The comments come ahead of MPs voting tomorrow on the Alcohol Reform Bill in Parliament to keep the purchase alcohol age to 18 or increase it to 20.
Prime Minister John Key has said he will vote for the split option: 18 in bars and 20 at off-licence liquor outlets.
Dr Crampton said that if there were problems with youth drinking culture, those problems were unlikely to be remedied by changing the drinking age.
But he has been criticised for his "very broad brush use of statistics".
Professor Doug Sellman of the National Addiction Centre said Dr Crampton's claims could lead to improper conclusions.
He said that while comparing the categories over a decade might not show a significant change in "hazardous drinking", it does not show the full picture.
"The whole body of evidence needs to be considered," he said.
"And in fact, the Law Commission examined the whole body of evidence during its major alcohol review of 2009/2010 and the overall conclusion is that there is an increase in alcohol-related harm from reducing the purchase age."
The Law Commission moved from initially suggesting a 18/20 split age of purchase to finally recommending a 20/20 purchase age.
