In an interesting decision, the Court of Appeal for Ontario took the unusual step of overturning an acquittal by a jury on a charge of first degree murder. The decision in R. v. Abbey, 2009 ONCA 624, is noteworthy for the extended analysis by Mr. Justice David Doherty on the scope of expert evidence, in this case the evidence of a sociologist knowledgeable in youth gang culture. Mr. Abbey was charged with the 2004 murder of a member of the Galloway Boys crew in Toronto. He was an admitted member of a rival gang, which was in the midst of a violent turf war with the Galloway Boys at the time of the murder. A few months after the murder, Mr. Abbey had a teardrop tattoo inscripted on his face. Based on interviews conducted with gang members over a 25 year practice, the expert witness was able to testify that inscription of the teardrop tattoo could mean that the person with the tattoo had killed a rival gang member. The trial judge had excluded the evidence from consideration by the jury as he considered it was not sufficiently reliable. The Court of Appeal overturned the decision and ordered a new trial. In the course of the decision, the Court made the following important comments.
It is fundamental to the adversary process that witnesses testify to what they saw, heard, felt or did, and the trier of fact, using that evidentiary raw material, determines the facts. Expert opinion evidence is different. Experts take information accumulated from their own work and experience, combine it with evidence offered by other witnesses, and present an opinion as to a factual inference that should be drawn from that material. The trier of fact must then decide whether to accept or reject the expert’s opinion as to the appropriate factual inference. Expert evidence has the real potential to swallow whole the fact-finding function of the court, especially in jury cases. Consequently, expert opinion evidence is presumptively inadmissible. The party tendering the evidence must establish its admissibility on the balance of probabilities: Paciocco & Stuesser at pp. 184, 193; S. Casey Hill et al., McWilliams’ Canadian Criminal Evidence, 4th ed., looseleaf (Aurora, Ont.: Canada Law Book, 2009), at para. 12:30.10.
The increased reliance on expert opinion evidence by both the Crown and defence in criminal matters is evident upon even a cursory review of the reported cases. Sometimes it seems that a deluge of experts has descended on the criminal courts ready to offer definitive opinions to explain almost anything. Expert evidence is particularly prevalent where inferences must be drawn from a wide variety of human behaviour: see, for example, R. v. McIntosh (1997), 35 O.R. (3d) 97 (C.A.), at pp. 101-103, leave to appeal to S.C.C. refused R. v. McCarthy,  1 S.C.R. xii [leave sought by second appellant in McIntosh, Mr. McCarthy]; David M. Paciocco, “Coping With Expert Evidence About Human Behaviour” (1999) 25 Queen’s L.J. 305, at pp. 307-308; S. Casey Hill et al. at para. 12:30.10; R. v. Olscamp (1994), 95 C.C.C. (3d) 466 (Ont. Ct. (Gen. Div.)), approved in R. v. Lance (1998), 130 C.C.C. (3d) 438 (Ont. C.A.), at para. 24; Ontario, The Commission on Proceedings Involving Guy Paul Morin: Report, vol. 1 (Toronto: Queen’s Printer, 1998), at pp. 311-24. As Moldaver J.A. put it in R. v. Clark (2004), 69 O.R. (3d) 321 (C.A.), at para. 107, a case involving the proposed expert evidence of a criminal profiler:
Combined, these two concerns [giving expert evidence more weight than it deserves and accepting expert evidence without subjecting it to the scrutiny it requires] raise the spectre of trial by expert as opposed to trial by jury. That is something that must be avoided at all costs. The problem is not a new one but in today’s day and age, with proliferation of expert evidence, it poses a constant threat. Vigilance is required to ensure that expert witnesses like Detective Inspector Lines are not allowed to hijack the trial and usurp the function of the jury. [Emphasis added.]
Despite justifiable misgivings, expert opinion evidence is, of necessity, a mainstay in the litigation process. Put bluntly, many cases, including very serious criminal cases, could not be tried without expert opinion evidence. The judicial challenge is to properly control the admissibility of expert opinion evidence, the manner in which it is presented to the jury and the use that the jury makes of that evidence…
It is not surprising that Dr. Totten’s opinion could not pass scientific muster. While his research, and hence his opinion, could be regarded as scientific in the very broad sense of that word, as used in McIntosh, Dr. Totten did not pretend to employ the scientific method and did not depend on adherence to that methodology for the validity of his conclusions. As his opinion was not the product of scientific inquiry, its reliability did not rest on its scientific validity. Dr. Totten’s opinion flowed from his specialized knowledge gained through extensive research, years of clinical work and his familiarity with the relevant academic literature. It was unhelpful to assess Dr. Totten’s evidence against factors that were entirely foreign to his methodology. As Professors Sales and Shuman put it in their text, Experts in Court: Reconciling Law, Science, and Professional Knowledge, at pp. 74-75: ‘[f]or non-scientific expert testimony, scientific validity is an oxymoron.’
Scientific validity is not a condition precedent to the admissibility of expert opinion evidence. Most expert evidence routinely heard and acted upon in the courts cannot be scientifically validated. For example, psychiatrists testify to the existence of various mental states, doctors testify as to the cause of an injury or death, accident reconstructionists testify to the location or cause of an accident, economists or rehabilitation specialists testify to future employment prospects and future care costs, fire marshals testify about the cause of a fire, professionals from a wide variety of fields testify as to the operative standard of care in their profession or the cause of a particular event. Like Dr. Totten, these experts do not support their opinions by reference to error rates, random samplings or the replication of test results. Rather, they refer to specialized knowledge gained through experience and specialized training in the relevant field. To test the reliability of the opinion of these experts and Dr. Totten using reliability factors referable to scientific validity is to attempt to place the proverbial square peg into the round hole.
As the decision of the Court of Appeal had the effect of overturning an acquittal, under the Criminal Code the accused now has the right to appeal directly to the Supreme Court of Canada. That Court will now be charged with the important responsibility of delineating the proper scope of expert evidence in the litigation process in Canada.