An expert deposition is intended to identify the opinions the witness expects to give at trial. When the expert later changes a supposedly final opinion or issues a materially different report, the court may prevent the new testimony from being introduced.

The Deposition Establishes the Expected Opinions

During deposition, an expert may be asked whether the opinions expressed are the only opinions the expert intends to offer at trial. An affirmative answer allows the attorneys to prepare cross-examination, decide whether another expert is needed, and evaluate settlement.

The expert should explain not only the conclusion but also the assumptions, calculations, records, and methods supporting it. A clear deposition record helps define the permitted scope of later testimony.

A Material Change Can Cause Unfair Surprise

An expert may not be permitted to present a materially different trial opinion after representing that the deposition opinions were final. The same concern can arise when an expert prepares an amended report after the deposition containing a new or changed conclusion.

Minor clarification is different from changing the substance of an opinion. The court must evaluate what changed and whether the opposing party had a fair opportunity to examine the new analysis.

Exclusion Depends on the Deposition Record

A request to exclude the changed opinion is strongest when the expert expressly confirmed that the deposition covered all intended opinions. If the expert clearly identified continuing work or reserved a limited issue, the analysis may be different.

The court’s decision is discretionary and fact-specific. The transcript, original report, amended report, calculations, and timing of the change are central to determining whether exclusion is appropriate.

The Change Should Be Addressed Promptly

A party who learns that an expert’s opinion has changed should not wait until the middle of trial to raise the issue. The attorneys may need to request additional discovery, seek an agreement limiting the testimony, or ask the court for pretrial relief.

The party offering the expert should disclose material changes rather than attempting to obtain a tactical advantage through surprise.

A California family-law attorney can compare the expert’s reports with the deposition testimony, assess whether the change is material, and seek a fair remedy that protects the client’s ability to prepare for trial.