even qualified to give such evidence. While he had the qualifications of a mental health clinician (the expertise that was accepted
by the trial judge), his qualifications were not considered in connection with the opinions sought to be elicited from him. Dr. Smith
was permitted to give opinion evidence related to the issue of
whether the alleged abuse occurred, even though none of Dr. Smith’s
qualifications demonstrated expertise in sexual abuse.
 Dr. Smith estimated that between 25 per cent and 30 per
cent of the inmates he saw had suffered from childhood sexual
abuse. However, the fact that Dr. Smith understood that many of
his patients had suffered from childhood sexual abuse does not, of
course, make him an expert in the field. While Dr. Smith had
expertise in treating prisoners with trauma, he did not have
particular expertise in childhood sexual abuse. Accordingly, Dr.
Smith was not qualified to offer an opinion about the problems
typical of survivors of sexual abuse, or as to the relationship between the alleged sexual assaults and Mr. Imeson’s subsequent
difficulties, including the commission of the first murder.
 In conclusion, I agree with the respondent that Dr. Smith’s
opinion evidence that was tendered on the issues of liability and
causation did not meet the threshold criteria to be admissible as
expert evidence, as the evidence was not necessary and Dr. Smith
did not have the required expertise. As that decides the threshold
question, I need not deal with other aspects of the threshold criteria. In particular, I note that the question of Dr. Smith’s impartiality in relation to the opinions he offered was not argued on
appeal and I will not therefore address that issue.
 While unnecessary to go further, I would also comment
briefly on the trial judge’s gatekeeping role under the second part
of the Mohan/White Burgess framework.
 Under the second part of the Mohan/White Burgess
framework, the trial judge must assess the benefits of admitting
the evidence against its potential risks. The cost-benefit analysis
to be undertaken as part of the trial judge’s role “is a specific
application of the court’s general residual discretion to exclude
evidence whose prejudicial effect is greater than its probative
value”: Bruff-Murphy, at para. 65.
 In this case, the admission of Dr. Smith’s opinion evidence
carried a number of risks to the trial process.
 One such risk was that the jury might conclude that
Dr. Smith’s testimony of what he was told by Mr. Imeson was
proof of the truth of Mr. Imeson’s narrative. The trial judge
addressed this risk with the hearsay caution.
 The admission of Dr. Smith’s opinion evidence presented
other risks to the trial process.