The opinion evidence of experts is not always admissible at the hearing of a motion or a trial.
The Ontario Divisional Court recently handed down its Decision in Mastermeter Products Canada Inc. v. Corporation of the City of North Bay, 2012 ONSC 1887 (CanLII). The hearing involved an application for judicial review of the City of North Bay’s award of a contract for the supply and installation of water meters. Mastermeter complained that it had been treated unfairly by the City in the course of its procurement process and lost out on the contract as a result.
While the Decision is primarily concerned with procurement issues, my interest in it is the Court’s ruling to exclude opinion evidence of an “expert” where the supposed expertise of the witness was on matters/issues within the expertise of the Judges hearing the application. The interesting bit for me is at paragraphs 21-23 of the Decision which read:
The Admissibility of an Expert Opinion
 Counsel for the applicant proffered an expert witness statement of Rishi Kumar, M.Sc. Eng, P.Eng. Mr. Kumar was retained to provide an opinion for this application for judicial review on the following question:
Whether or not the bid process under RFP 2009-006 was conducted responsibly and with the requisite degree of fairness, openness and transparency applicable to major competitive procurement process.
 Mr. Stieber, counsel for the City, objected to the admissibility of the proffered opinion on the ground that it does not meet one of the criteria for the admission of expert evidence from R. v. Mohan, 1994 CanLII 80 (SCC),  2 S.C.R. 9, in that it is not necessary to assist the court.
 We agree that the proffered opinion does not meet the necessity criterion because the Court can form its own conclusion about the fairness of the City’s procedure without the assistance of the proffered expert testimony. Therefore, the affidavit of Mr. Kumar was struck at the outset of the hearing.
Without getting into details of the rules and jurisprudence around expert evidence, as a general statement, the Court is to exercise a “gatekeeper” function - admitting the opinion evidence of experts where the subject matter of the evidence is outside of the expertise of judges (and provided it meets certain other criteria) and excluding the rest.
Legal theory aside, one of the reasons that this gatekeeper function is so important is that expert evidence can be very expensive and can drive up the cost of litigation substantially. As such, only that expert opinion evidence which is helpful and necessary to the court to decide the case should be admitted. This is particularly true of construction litigation where expert opinion evidence is very, very common and the lawsuit often evolves into a “battle of the experts”.
Too often, in my view, courts are prone to allowing parties to introduce “expert” evidence in areas where the judge has sufficient expertise and does not require assistance. In my view, if litigants can have the confidence that the court will exercise the gatekeeper function properly, as it did in this case, when an opposing party serves an “expert” report that is unhelpful and unnecessary to the court in deciding the issue for which the evidence is introduced, the recipient of that report can more confidently chose to avoid the time and significant expense of responding the the report and simply seek its exclusion at the trial or hearing.