How Software Engineering Expert Witnesses Get Excluded Under Daubert — and How to Survive the Cross

Daubert is not a medicine problem. Under Kumho Tire and the 2023 amendment to Federal Rule of Evidence 702, the trial court's gatekeeping applies to every form of specialized testimony — software engineering included. A 20-year study of 2,842 challenges to non-medical experts found that roughly half of those opinions were excluded or partially excluded, and the single most-cited reason was “unreliable methodology.”

The exclusion rarely happens in a written motion alone. It is built, piece by piece, in the deposition cross-examination — where opposing counsel walks a software engineering expert into conceding scope, methodology, or an assumption that unravels the whole opinion. Here are the three traps, and how a prepared expert answers each one.

The three ways software engineering experts lose ground

Scope: testifying outside your lane

The cross-examiner's question sounds simple:

You opine the software was defectively built — but you've never worked in this specific industry's software, have you?

Why it works: The domain scope attack. Anchor to engineering standards and the requirements, not to identical industry experience.

A stronger answer: “My opinions rest on accepted software-engineering practices and the contract requirements, which apply across industries; I cited the standards and the specific requirements at issue.”

Methodology: the reliability attack

The cross-examiner's question sounds simple:

Your conclusion relied on the production logs — you didn't have access to the full source-code repository, did you?

Why it works: Methodology / data access. Bound the opinion to what you could inspect and flag the gaps.

A stronger answer: “I analyzed the logs and the code I was provided and explicitly noted any conclusion that would be confirmed or refined by the full repository, which I requested.”

Assumptions: the one premise that sinks the opinion

The cross-examiner's question sounds simple:

You assume the requirement was clearly specified — but the contract is silent on this behavior, isn't it?

Why it works: The requirement-assumption trap. Separate what the contract required from what good practice would suggest.

A stronger answer: “Where the contract was silent, I analyzed against accepted industry practice and the documented requirements, and I distinguished contractual obligations from best-practice expectations.”

How to prepare for the cross before you're sworn in

Every one of those traps is defeatable — but not by reading your report one more time. The experts who survive the cross have done three things:

• Rehearsed the cross-examination out loud, repeatedly, against a realistic examiner — so the scope concession, the methodology defense, and the assumption hedge are second nature.
• Mastered the record, so that when counsel asks them to recall the one line buried in thousands of pages of the source code, logs, and requirements docs, they can produce it in seconds rather than fumble.
• Stress-tested the report against FRE 702 — finding the reliability gaps before opposing counsel does.

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