Estimates vary on the number of Iraqi civilians killed since 2003
An academic whose estimates of civilian deaths during the Iraq war sparked controversy has been criticised for not fully co-operating with an inquiry.
Gilbert Burnham said in the Lancet medical journal in 2006 that 650,000 civilians had died since 2003 - a figure far higher than other estimates.
A polling association in the US said Dr Burnham had refused to supply "basic facts" for its inquiry into his work.
It did not comment on the accuracy of his conclusion.
The American Association for Public Opinion Research (AAPOR)began investigating Dr Burnham's work in March 2008 after a complaint by one of its members.
His research was based on a survey of Iraqi households and concluded that by July 2006 about 655,000 Iraqi civilians had died as a result of the US-led invasion.
The Iraqi government does not keep precise records of civilians killed and neither do US forces, but in 2006 the Iraqi health ministry estimated that between 100,000 to 150,000 civilians had died.
The AAPOR's executive council said in a statement carried by the Associated Press news agency: "When asked to provide several basic facts about this research, Burnham refused."
It said it wanted to know the wording of questions asked and instructions and explanations given to respondents.
"Dr Burnham provided only partial information and explicitly refused to provide complete information about the basic elements of his research," said Mary Losch, chair of the association's standards committee.
She added that Dr Burnham's refusal to co-operate "violates the fundamental standards of science, seriously undermines open public debate on critical issues and undermines the credibility of all survey and public opinion research."
A spokesman for the Johns Hopkins Bloomberg School of Public Health, where Dr Burnham works, said they were disappointed AAPOR had said he violated the code of ethics.
However, the spokesman pointed out to AP that neither the researcher nor the school were members of the association.
The level of civilian casualties in Iraq has been a controversial issue ever since the US-led invasion of 2003.
For Dr Burnham's study, researchers spoke to more than 1,800 families comprising 12,800 people, comparing mortality rates in selected areas before and after the invasion.
Its conclusion was undermined by allegations that the number of people surveyed was too small and that the authors may have inflated the figures for political reasons.
The Lancet said it had no comment.
The independent Iraq Body Count, which counts only confirmed deaths, currently has a range of between 90,556 and 98,850.