In New Jersey, Expert’s “Net Opinions” Are Not Created Equal

Expert witnesses play a critical role in helping parties prove their cases in court. Experts are often brought in to testify about complex technical or scientific matters that are outside the scope of a layperson's knowledge. However, not all expert opinions are admissible in court. In New Jersey, expert opinions that fail to meet certain criteria are considered "net opinions" and are inadmissible as evidence.

In New Jersey, Expert’s “Net Opinions” Are Not Created Equal

BySeth Mills, J.D.


Published on January 26, 2024

In New Jersey, Expert’s “Net Opinions” Are Not Created Equal

What is a Net Opinion?

A net opinion is an expert opinion that lacks a rational basis in the factual record or fails to articulate the reasoning or methodology behind the expert's conclusions. In other words, the expert’s conclusion alone is not admissible. When an expert offers a net opinion, the Net Opinion Rule requires the trial court to exclude it from evidence.

Why is the Net Opinion Rule Important?

The Net Opinion Rule ensures that expert testimony is based on sound reasoning and methodology and is not simply the expert's subjective beliefs or assumptions. This helps prevent juries from being misled by unreliable or speculative testimony. It also helps ensure that parties are not unfairly prejudiced by the introduction of expert testimony that lacks a rational basis in the record.

How is the Net Opinion Rule Applied?

To determine whether an expert opinion is a net opinion, the court will examine whether the opinion is based on a reasonable degree of scientific, technical, or specialized knowledge. The court will also look at whether the expert has applied the appropriate methodology to reach their conclusions. If the court determines that the expert has failed to provide a sufficient factual basis or methodology for their opinion, then the expert’s opinion will be excluded from evidence.

The Net Opinion Rule does not require experts to be infallible or to have absolute certainty in their opinions. Rather, it simply requires them to provide a rational basis for their opinions and to apply a recognized methodology in reaching their conclusions. If an expert is able to provide this basis, their opinion should be admissible in court.

The NJ Net Opinion Rule is applicable in all types of cases where expert testimony is offered. This can include civil and criminal cases, as well as administrative and regulatory proceedings. The rule applies to all types of expert witnesses, including medical experts, scientific experts, engineering experts, financial experts, and more. Any expert opinion offered in a New Jersey court must comply with the Net Opinion Rule and provide a sound basis for the expert's conclusions.

Cases Illustrating the Net Opinion Rule

In a negligence/product liability case, the court excluded a safety engineering expert’s testimony regarding a video of the plaintiff’s accident because the cause of the accident was not visible on video. The expert relied on the records of previous elevator work orders, and did not offer any drawings or address any other possible causes of the alleged elevator malfunction.

In an attorney negligence action, the court excluded an expert’s opinion that was based on anecdotal evidence from another case in which the expert offered testimony.

In a recent asbestos exposure case, the trial court granted summary judgment in favor of an asbestos remediator after excluding the plaintiff’s expert’s testimony as a “net opinion”. The court found that the expert’s opinion that the remediator was negligent was not based on the facts in the record and did not address other possible causes for the contamination.

Similarities to Daubert and Frye Standards

The Net Opinion Rule is analogous to the Daubert and Frye standards followed in other state and federal courts. The goal of each of these rules is to ensure that expert testimony is based on reliable methodology and objective facts.

The Daubert standard, followed by federal courts and some state courts, requires judges to evaluate the reliability and relevance of expert testimony based on several factors. This includes whether the expert's methodology has been tested, whether the methodology has been subject to peer review and publication, and whether the methodology has been generally accepted in the relevant scientific community.

The Frye standard, which is followed by some states, requires that expert testimony be based on scientific principles that are generally accepted in the relevant field. This standard focuses on whether the methodology used by the expert is widely accepted within the scientific community, rather than on whether the methodology has been subjected to testing or review.

Overall, the Net Opinion Rule requires experts to provide reasoned explanations for their opinions. In preparing for litigation, attorneys should choose experts who are able to provide and describe a rational basis for their opinions, and prepare expert witnesses well so their explanations are communicated clearly.

About the author

Seth Mills, J.D.

Seth Mills, J.D.

Seth Mills, J.D., a career counselor at New York Law School, has a substantial background in legal education and public interest initiatives. Currently serving as the Director of Public Interest & Pro Bono Initiatives and an Adjunct Professor for the Law Office Externship Seminar at New York Law School, Seth focuses on guiding law students in their professional development and legal externship experiences.

Prior to these roles, Seth was a Legal Content Writer for the Expert Institute, contributing to the development and curation of legal content. At, Seth held multiple positions, including Senior Program Attorney and Managing Blog Editor, where he was responsible for creating legal educational materials and managing legal publications.

Seth's legal career began as an Associate Attorney at Sterling Analytics Group, providing a foundation in practical legal work. Additionally, Seth volunteered as a Policy Advocate with the Police Reform Organizing Project (PROP), demonstrating a commitment to public interest law.

In terms of education, Seth earned a J.D. cum laude from New York Law School, where they were involved in NYLS OUTlaws and the Criminal Law Society. Seth also holds a Bachelor of Arts in Linguistics from Bard College at Simon's Rock. Their educational and professional experiences reflect a deep commitment to legal education, public interest law, and the mentoring of future legal professionals.

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