The rules of evidence allow for three expert witnesses to be called at trial. The plaintiff in Leonard v. Kline , ONSC 2730 (S.C.J.) sought leave to call nine expert witnesses at her upcoming jury trial. The list of proposed experts included a psychiatrist, psychologist, vocational expert, vocational rehabilitation consultant, accountant/actuary and others.
The issue at the plaintiff’s upcoming trial was her earning capacity. The plaintiff sought to have each expert witness give an opinion on whether she would be able to engage in gainful employment. The plaintiff’s argument was two-fold: 1) each expert approaches the issue from a different area of expertise; and 2) the jury should know what the “weight of expert” evidence is on the issue.
The defendant argued that this would be duplicitous [sic - duplicative]. The defendant only intended to call two expert witnesses.
Ellies J. did not agree with the plaintiff’s “weight of expert evidence” argument expressing his concern with trials becoming battles of the experts. He went on to consider the eight factors listed in Burgess (Litigation Guardian of) v. Wu ,  O.J. No. 929. His decision focused on factor seven – the degree to which there is duplication in the proposed opinions of different experts.
Upon determining that some of the proposed expert witnesses were duplicitous [sic - duplicative]. , Ellies J. proceeded to divide them into groups based on shared opinions, whether they prepared joint reports, and whether they used similar tests upon the plaintiff in which their opinion was based. The plaintiff was then given the option to choose one expert witness from each group.
This decision seems to be a good example of the court fulfilling its "gatekeeper" role with respect to experts.