When you are a parent, you are often tempted to answer the question "why?" with "because I say so." Experts shouldn't get away with that in court.

The New Jersey Supreme Court recently addressed the scope of the so-called “Net Opinion Rule,” which precludes expert testimony that does not have a sufficient basis. See Townsend v. Pierre, 221 N.J. 36, 110 A.3d 52 (March 12, 2015).  The case involved a motorcycle vs. auto collision, so let's get right to the analysis.

When a New Jersey court determines the admissibility of expert testimony, N.J.R.E. 702 and N.J.R.E. 703 frame its analysis. N.J.R.E. 702 imposes three core requirements for the admission of expert testimony: (1) the intended testimony must concern a subject matter that is beyond the ken of the average juror; (2) the field testified to must be at a state of the art such that an expert’s testimony could be sufficiently reliable; and (3) the witness must have sufficient expertise to offer the intended testimony.  Creanga v. Jardal, 185 N.J. 345, 886 A.2d 633 (2005) (quoting Kemp ex rel. Wright v. State, 174 N.J. 412, 424, 809 A.2d 77 (2002)).

N.J.R.E. 703 addresses the foundation for expert testimony. It mandates that expert opinion be grounded in facts or data derived from (1) the expert’s personal observations, or (2) evidence admitted at the trial, or (3) data relied upon by the expert which is not necessarily admissible in evidence but which is the type of data normally relied upon by experts. State v. Townsend, 186 N.J. 473, 494, 897 A.2d 316 (2006).  The net opinion rule is a corollary of  N.J.R.E. 703, which forbids the admission into evidence of an expert’s conclusions that are not supported by factual evidence or other data. The rule requires that an expert give the why and wherefore that supports the opinion, rather than a mere conclusion.  Borough of Saddle River v. 66 E. Allendale, LLC, 216 N.J. 115, 144, 77 A.3d 1161 (2013) (quoting Pomerantz Paper Corp., supra, 207 N.J. at 372, 25 A.3d 221).

The net opinion rule, said the court, is not a standard of perfection. The rule does not mandate that an expert organize or support an opinion in a particular manner that opposing counsel deems preferable. An expert’s proposed testimony should not be excluded merely because it fails to account for some particular condition or fact which the adversary considers relevant. Creanga, supra, 185 N.J. at 360, 886 A.2d 633 (quoting State v. Freeman, 223 N.J.Super. 92, 116, 538 A.2d 371 (App.Div.1988), certif. denied, 114 N.J. 525, 555 A.2d 637 (1989)). The expert’s failure to give weight to a factor thought important by an adverse party does not reduce his testimony to an inadmissible net opinion if he otherwise offers sufficient reasons which logically support his opinion. Rosenberg v. Tavorath, 352 N.J.Super. 385, 402, 800 A.2d 216 (App.Div.2002). Such omissions may be a proper subject of exploration and cross-examination at a trial. Rubanick v. Witco Chem. Corp., 242 N.J.Super. 36, 55, 576 A.2d 4 (App.Div.1990), modified on other grounds, 125 N.J. 421, 593 A.2d 733 (1991).

The net opinion rule, however, mandates that experts be able to identify the factual bases for their conclusions, explain their methodology, and demonstrate that both the factual bases and the methodology are reliable. An expert’s conclusion must be excluded if it is based merely on unfounded speculation and unquantified possibilities.  So, when an expert speculates, he ceases to be an aid to the trier of fact and becomes nothing more than an additional juror. By definition, unsubstantiated expert testimony cannot provide to the factfinder the benefit that N.J.R.E. 702 envisions: a qualified specialist’s reliable analysis of an issue “beyond the ken of the average juror.” Given the weight that a jury may accord to expert testimony, a trial court must ensure that an expert is not permitted to express speculative opinions or personal views that are unfounded in the record.  And a party’s burden of proof on an element of a claim may not be satisfied by an expert opinion that is unsupported by the factual record or by an expert’s speculation that contradicts that record. Here, the accident occurred when defendant turned left at an intersection controlled by a stop sign. The plaintiffs argued that the proximate cause of the accident was negligently maintained overgrown shrubbery, which blocked the view of oncoming traffic.  Their expert was well qualified in engineering, and could have opined as to the design of the intersection. But, said the court, with respect to the issue of causation, the opinion diverged from the only record evidence. He did not apply his engineering expertise to present empirical evidence undermining the undisputed and corroborated testimony that when the driver turned left, her view of traffic was unimpeded. He took no measurements to demonstrate the line of vision of a driver located at the point at which she recalled making her left turn. Instead, the expert analyzed the impact of the shrubbery on the line of vision of a driver stopped behind the stop sign, explaining that placement of a stop sign and negligent property maintenance proximately caused the accident. In an attempt to reconcile his opinion with the testimony, the expert simply reconstituted the facts. He asserted that the driver's testimony about her accident was simply wrong. In this crucial respect, the expert's proposed expert testimony was indeed an inadmissible net opinion.