Insights
What makes an expert report admissible
The motions that succeed against expert testimony are not usually the ones attacking credentials. They attack the distance between what the expert relied on and what the expert concluded — and that distance is created, or closed, in the way the report is written.
The gap that exclusion motions actually target
The analytical gap between the material relied on and the conclusion drawn. A causation opinion citing literature about a different exposure, a damages model projecting from a baseline the documents do not show, an assumed fact no witness established — these are the recurring shapes.
Each shares a structure: the expert is qualified, the method is respectable, and the conclusion does not follow from what is actually in the record. That is a reasoning problem rather than a credentials problem, and it is not cured by adding to the CV.
It is also, importantly, a problem that is visible on the face of the report before anyone files a motion. An opinion whose inferential steps are stated can be checked; one that moves from a summary of records to a conclusion in a single paragraph cannot, and the missing steps are exactly what the motion will say do not exist.
State the bases, and state them specifically
Every document, record, test result, site observation, and item of literature the opinion rests on, identified individually. Not 'the medical records' but which records, and not 'the literature' but which papers and what they actually address.
Specificity here does two things. It lets the court perform the examination the applicable standard directs it to perform, and it makes the opinion checkable, which is the quality that distinguishes expert evidence from assertion.
It also protects against the most avoidable form of attack. Where the bases are listed, opposing counsel cannot credibly suggest the expert relied on something they did not, and the expert cannot be walked into adopting a document they never saw.
Name the method and say why it fits
Identify the methodology by name, explain why it is appropriate to this question, and — where the forum applies a general-acceptance test — establish its standing in the field rather than assuming it.
How much weight this carries depends on the forum. Washington applies the Frye general-acceptance test to novel scientific evidence, which asks about the standing of the method itself. The federal courts apply FRE 702, which since its December 2023 amendment squarely examines whether the opinion reflects a reliable application of the methodology to the facts. California's Sargon analysis and Oregon's OEC 702 framework each ask something related but distinct.
A report that addresses both the standing of the method and the rigour of its application satisfies all four without needing to guess which will be applied — and that is the sensible default where removal is possible.
Set out the inferential steps in sequence
Not the conclusion and its support, but the path: this record shows X, X together with Y makes Z more likely than the alternatives, and here is why the alternatives are less consistent with the record.
This is the section most reports compress and the one that most determines whether the opinion survives. An expert who has written the steps has already done the work a cross-examination will demand; an expert who has not will do it live, under pressure, for the first time.
Alternative explanations deserve explicit treatment rather than silence. An opinion that names the obvious competing theory and explains why the record fits it less well is far stronger than one that ignores it — and in a jurisdiction with simultaneous exchange, where the opposing report will not be seen first, addressing the alternatives proactively is the only opportunity available.
Acknowledge the limits
State what the opinion does not establish, what a fuller record might change, and where the evidence supports a range rather than a point. An expert who concedes limits in the report is harder to dismantle than one conceding them for the first time on cross-examination.
There is a natural resistance to this — it feels like weakening the opinion. It is the opposite. The concessions are going to be extracted either way; the only variable is whether they appear as a considered statement in the expert's own words or as an admission drawn out by opposing counsel in front of the finder of fact.
An opinion that claims more than the record supports is also the one most exposed to the analytical-gap attack, because the overclaim is precisely the gap. Stating the limits is not a concession to the other side. It is how the rest of the opinion is made credible.
Frequently Asked Questions
Less often than expected. Qualification challenges succeed mainly where an expert is offered just outside their actual practising field. The more common successful attack is on the analytical gap between the material relied on and the conclusion drawn.
Yes, and explicitly. Naming the obvious competing explanation and showing why the record fits it less well is materially stronger than silence — and in a simultaneous-exchange jurisdiction like California it is the only opportunity, since the opposing report will not be seen first.
No. The concessions will be extracted at deposition regardless; the only variable is whether they appear as a considered statement in the expert's own words or as an admission drawn out by opposing counsel. An opinion that claims more than the record supports is the one most exposed.
In practice yes. A report that identifies its bases specifically, names and justifies the method, sets out the inferential steps, addresses alternatives, and states its limits does well under Sargon, Frye and ER 702, the OEC 702 framework, and FRE 702 alike.
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