VANCOUVER - The British Columbia judge asked to assess Canada's law against polygamy began hearing from his first witness on Tuesday, in a constitutional reference case that will clearly come down to a battle of experts.

The actual testimony by Angela Campbell, a law professor at McGill University, was preempted by debate over whether she's qualified to offer expert evidence at all.

Campbell sat in the witness stand as lawyers meticulously dissected her resume and research experience for several hours, a scene likely to be repeated again and again as experts from both sides of the debate offer their opinions on the pros and cons of a polygamous lifestyle.

The legal arguments lasted until early in the evening, when the judge allowed Campbell's testimony, which will begin Wednesday.

Introduced in court as a legal scholar and researcher who has studied the ban on polygamy and Bountiful in particular, Campbell visited the southeastern B.C. community in 2008 and 2009 to interview women as part of her research.

She's already filed two affidavits with the court outlining her opinion that the prohibition against polygamy is harmful.

"The criminalization of polygamy has had adverse outcomes for Bountiful's residents," Campbell wrote in her affidavit. "That is, residents of Bountiful feel ashamed, stigmatized and highly anxious because their way of life is branded as criminal."

She also said the women she spoke with told her that marriages involving adolescent girls are discouraged, and some women were allowed input into who they marry. She said if there are harms associated with polygamy, the law appears unable to prevent them and instead makes it more difficult for people living in polygamous communities to seek help.

But Campbell's expertise was challenged by lawyers for the provincial and federal governments, as well as several interveners including the advocacy group Stop Polygamy in Canada.

They noted Campbell was trained in law, and not in sociology, psychology or ethnography, making her observations outside her area of expertise.

They also suggested Campbell wasn't qualified in the sort of qualitative, interview-based research she conducted in Bountiful. She currently teaches a graduate-level research course at McGill.

Campbell was called as a witness by George Macintosh, a lawyer appointed as what is called an amicus, who will argue against the polygamy law.

Craig Cameron, who represents the federal government, argued the transcripts of Campbell's initial interviews should be entered into evidence, but her interpretations of them should not.

"The amicus has failed to establish that Prof. Campbell is qualified to give expert opinion evidence," said Cameron. "To the extent that Prof. Campbell is qualified to give expert evidence, the evidence in these reports falls outside her expertise."

Tim Dickson, a lawyer working alongside the government-appointed amicus, noted Campbell has received several federal government research grants, and her research proposals and the resulting papers are all peer-reviewed.

"If the court is to consider the existing academic research on polygamy, it will want to consider Prof. Campbell's research -- it is the best research on polygamy in Canada to date," said Dickson.

Chief Justice Robert Bauman said Campbell will be qualified as an expert witness and she'll be allowed to testify. He didn't give his reasons.

The B.C. criminal justice branch charged the leaders of Bountiful, Winston Blackmore and James Oler, with practising polygamy, but the charges were quashed in court because several legal opinions had recommended against such charges previously.

The province then asked the B.C. Supreme Court last year to examine whether the prohibition against polygamy violates the Charter of Rights and Freedoms, as Blackmore and Oler claim.

The provincial and federal government maintain that polygamy inherently fosters sexual abuse and discrimination against women. Those arguing against the law argue that criminalizing multiple marriages violates the guarantee of religious freedom and stigmatizes people living in polygamous communities.

In addition to experts lining up in both camps, the court will hear testimony from people currently living in polygamous marriages, as well as women and children who have left polygamous communities.

Earlier in the day, Bauman delayed his decision about whether video affidavits from 14 ex-wives and children from polygamous relationships can be broadcast publicly. Their content has already been reported, but the Crown does not want them broadcast on TV or the Internet unless witnesses specifically consent.

One of the witnesses, Ruth Lane, complained after an edited clip of her testimony appeared on a local newspaper website.

That matter was put off until Thursday, when Lane is expected to address the court by telephone.