Every once in a while, a journalist will claim that the average age of entry into prostitution is 14.

It's an effective argument for prohibitionists, who would like to ban men from purchasing sex.

However, an Ontario Superior Court decision last month should make people question that assertion the next time it appears in print.

In a constitutional challenge against Canada's prostitution laws, Justice Susan Himel poured cold water over an expert witness's suggestion that the average sex worker begins plying her trade at the age of 14.

Himel's ruling questioned the testimony of University of Ottawa sociology and anthropology professor Richard Poulin.

"His research has focused on prostitution, human trafficking, pornography, and the dynamics of the global sex trade, with a particular focus on minors," Himel wrote, adding that Poulin supports the abolition of prostitution based on his research.

"As well, during cross-examination, it was revealed that some of Dr. Poulin’s citations for his claim that the average age of recruitment into prostitution is 14 years old were misleading or incorrect," the judge noted.

Poulin also swore in an affidavit that serial killers have targeted prostitutes working at indoor sites. Himel, however, stated in her ruling that "his sources do not appear to support his assertion."

"I found it troubling that Dr. Poulin stated during cross-examination that it is not important for scholars to present information that contradicts their own findings (or findings which they support)," Himel added.

Poulin's affidavit also claimed that "physical and sexual violence in prostitution is substantial, regardless of the legal regime in place". Under cross-examination, he "defined violence as meaning a systemic power imbalance", Himel commented in her ruling.

Without naming names, Himel also wrote: "I find that some of the evidence tendered on this application did not meet the standards set by Canadian courts for the admission of expert evidence. The parties did not challenge the admissibility of evidence tendered but asked the court to afford little weight to the evidence of the other party."

In a recent e-mail to the Vancouver Sun, Simon Fraser University criminology researcher John Lowman pointed out that the Crown's factum in the case cited only one Canadian study indicating that the average age of entry might be as low as 14 years of age.

Lowman, who has studied the consequences of Canada's prostitution laws for decades, noted that this paper by Sue McIntyre "used a purposive sampling strategy that sought to include only persons who entered prostitution as children or youth".

As a result of this methodology, Lowman maintained that it couldn't be generalized to the entire field of prostitution. He also stated in his e-mail that other Canadian studies have reported higher ages of entry.