Short answer. Rule 133, Section 5 gives the court wide discretion, guided by whether the opinion rests on sufficient facts or data, whether it results from reliable principles and methods, whether the expert actually applied those methods reliably to this case's facts, and any other factor the court finds helpful in reaching that determination.
What the law says
the court has a wide latitude of discretion in determining the weight to be given to such opinion
Rule 133, Section 5 — Weight to be given opinion of expert witness. how determined. Read the full provision →
What the law says
Whether the opinion is based upon sufficient facts or data: (b) Whether it is the product of reliable principles and methods: (c) Whether the witness has applied the principles and methods reliably to the facts of the case
Rule 133, Section 5 — Weight to be given opinion of expert witness. how determined. Read the full provision →
Discretion is the starting point, not a rubber stamp
Section 5 does not hand an expert's conclusion automatic weight simply because the witness qualifies as an expert. It gives the court a wide latitude of discretion in determining the weight to be given to such opinion. An expert being allowed to testify, and that testimony being given significant weight in deciding the case, are two separate questions — admissibility gets the opinion in front of the court; this section governs how much the court trusts it once it is there.
The three factors aimed at the opinion's reliability
The court is directed to consider whether the opinion is based upon sufficient facts or data, whether it is the product of reliable principles and methods, and whether the witness has applied the principles and methods reliably to the facts of the case. These three build on each other: an opinion can rest on a sound methodology in the abstract, yet still deserve less weight if the expert did not actually apply that methodology carefully to the specific facts of the case at hand.
The open-ended fourth factor
Beyond those three, the court may also weigh such other factors as the court may deem helpful to make such determination. This keeps the list from being an exhaustive checklist — an expert's qualifications, potential bias, the consistency of the opinion with other evidence in the case, and similar considerations can all legitimately factor into how much a court ultimately relies on what the expert said, on top of the three named factors.
What this means for a party relying on expert testimony
Simply presenting a qualified expert is not enough to guarantee the opinion carries real weight. A party wants to be able to show the data or facts the expert actually relied on, the soundness of the method used, and that the method was properly applied to this case's specific facts — because those are precisely the questions the court is directed to ask when deciding how seriously to take the conclusion the expert reached.
Related provisions
- Rule 133, Section 5 — Weight to be given opinion of expert witness. how determined
- Rule 133, Section 4 — Circumstantial evidence, when sufficient
- Rule 133, Section 6 — Substantial evidence