Rule 26 Expert Report Requirements

The six items the report must contain

Rule 26(a)(2)(B) applies to a witness retained or specially employed to provide expert testimony, and to a party's employee whose duties regularly involve giving expert testimony. That witness must produce a signed written report. The rule lists six items and uses the word must for all of them:

1. (i) a complete statement of all opinions the witness will express and the basis and reasons for them;
2. (ii) the facts or data considered by the witness in forming them;
3. (iii) any exhibits that will be used to summarize or support them;
4. (iv) the witness's qualifications, including a list of all publications authored in the previous 10 years;
5. (v) a list of all other cases in which, during the previous 4 years, the witness testified as an expert at trial or by deposition;
6. (vi) a statement of the compensation to be paid for the study and testimony in the case.

Two of those get transposed constantly, so state them separately. Item (iv) is qualifications, including all publications authored in the previous ten years. Item (v) is all other cases in which the witness testified as an expert at trial or by deposition during the previous four years. Publications: ten. Testimony: four. I have seen the numbers reversed in served reports and in firm templates, and the correction always arrives in front of the person you would least like to hear it from. The rule text is on Cornell's copy of Rule 26.

Why “facts or data considered” is wider than it looks

The rule requires disclosure of “the facts or data considered by the witness in forming them.” Not relied upon. Considered is the larger set: material examined and set aside, queries that returned nothing useful, exports superseded by a later pull, and everything counsel sent whether or not any of it survived into the opinion.

For many experts that distinction is close to academic, because the record is a fixed set of documents the parties produced. In search work it is not, because most of the raw material is generated on demand, in volume, by the expert. A single matter routinely involves crawls of the site at several dates using crawling software — a program that requests every URL on a site and records the status code, title, directives, and links it finds; performance exports from Google Search Console, the reporting property for a verified site showing the queries, impressions, clicks, and positions Google recorded; session exports from an analytics platform; raw server or CDN access logs, parsed and filtered; third-party index pulls; and API calls that return a different answer the next time they run.

Every one of those is a fact or datum considered. Where the opinion rests on a filtered subset, the filter is part of the disclosure and the unfiltered pull is part of what was considered. An expert who produces the four charts that reached the report and nothing behind them has produced the conclusion and withheld the record. In my experience the failure is not concealment. Nobody wrote down what was run.

The work log that makes item (ii) survivable

The answer is unglamorous and it has to begin on the first day of the engagement, not the week the report is due: an ordered work log, kept contemporaneously, recording every data pull as it happens. At minimum:

• what was pulled, named in the tool's own terms;
• the date range requested and the date the pull was made, which are different values and matter because most search data is a moving window;
• the property, view, filter, segment, or query string used, stated precisely enough that another analyst could re-run it;
• the file the pull produced, named so that file and log entry point at each other;
• the provenance: first-party from the client's own property, third-party estimate, or supplied by counsel;
• what became of it, including the entry “examined, not used.”

Two things fall out of a log kept that way. Production: item (ii) becomes an export rather than a reconstruction, and reconstruction after the fact is where omissions come from. And reliability: a documented, re-runnable pull turns an experience-based judgment into a method somebody else can test. The practices that satisfy the disclosure rules are, with few exceptions, the practices that survive a reliability challenge. Keep anything counsel supplied in its own identified place in the log; the reason lives in Rule 26(b)(4)(C).

The ten-year publication list, and why practitioners fail it

Item (iv) requires qualifications “including a list of all publications authored in the previous 10 years.” For an academic that is a curriculum vitae section that already exists. For a working search practitioner it can be enormous and it is scattered: posts on a personal site and a firm site, trade-press bylines, conference decks, webinar recordings, guest posts on sites that have since changed owners, columns in publications that have folded, and long technical answers in industry forums.

The consequence of an incomplete list is not a technical foul. Opposing counsel will find the omitted item. This is a field whose practitioners publish constantly, publicly, and under their own names, and the archive of what they published is itself searchable — that is the subject matter of the discipline. An expert whose report says one thing and whose forgotten post from six years ago says close to the opposite will be shown the post, and the cross that follows is only half about the inconsistency. The other half is the list: you swore this report was complete, and this is not on it.

Maintain the list continuously rather than assembling it at report time, keep archived copies because publications disappear, and treat the ten-year boundary as rolling. The same discipline applies to the four-year testimony list under item (v), the artifact nobody in this vertical publishes voluntarily and the one opposing counsel wants most, because it indexes every prior opinion the witness has given.

Opinions, basis, and exhibits — where search reports go thin

Item (i) requires “a complete statement of all opinions the witness will express and the basis and reasons for them.” The recurring failure in a search report is not a missing opinion. It is a stated opinion whose reasoning has been compressed into a sequence: traffic fell, the defendant did something, therefore the defendant caused the fall. That is a chronology, not an argument. The basis and reasons have to include why the alternatives were rejected — the concurrent core update, meaning a broad announced change to Google's ranking systems; the seasonal pattern that repeats in prior years; the site migration; the competitor's move; the tracking change that altered what was measured rather than what happened.

The disclosure consequence and the admissibility consequence run together. An opinion whose stated basis omits the alternatives is incomplete under item (i) and exposed on reliability, because the method described does not support the inference drawn. An expert explaining a confound for the first time at deposition has conceded that the report lacked the basis and reasons the rule asked for.

Item (iii) requires “any exhibits that will be used to summarize or support” the opinions, which in a search matter means charts built from very large exports. Two disciplines apply. Every chart should map to a named file in the work log, with the transformation between file and chart stated — the filter, the aggregation, the smoothing, the excluded rows — because a chart whose underlying export cannot be located is a chart whose numbers cannot be checked. And annotation matters: a line chart of organic sessions with a vertical rule at a date is a summary, while the same chart with that rule labeled “defendant's conduct” is an argument the chart does not prove.

Non-retained and hybrid witnesses under (a)(2)(C)

Not every expert opinion arrives with a report. Rule 26(a)(2)(C), added in 2010, governs the witness who is not required to provide one. That disclosure must state “(i) the subject matter on which the witness is expected to present evidence under Federal Rule of Evidence 702, 703, or 705; and (ii) a summary of the facts and opinions to which the witness is expected to testify.” Subject matter, and a summary. That is the whole disclosure.

The provision closed a gap where treating physicians and employee witnesses were offered with no expert disclosure at all. In search litigation it is how the other side's in-house SEO director or agency account manager arrives — two sentences in place of six items.

Often that is legitimate. Someone who ran a migration can testify to what they did, and for a technical employee the line between percipient observation and opinion is genuinely blurred. But measure what the lighter disclosure leaves out: no complete statement of opinions, no basis and reasons, no facts-or-data-considered production, no publication list, no testimony list, no compensation statement. If a (C) witness is going to opine on causation — that a competitor's conduct caused a ranking loss, that an agency's work fell below what the field expected — a summary is doing work it was not built for. A retained expert is frequently the person who explains to counsel what a given (C) disclosure covers and where it crosses from what the witness did into what the witness concluded.

Timing, and the report as a fixed position

Absent a stipulation or court order, Rule 26(a)(2)(D) sets expert disclosures at least 90 days before the date set for trial, and a disclosure intended solely to contradict or rebut evidence on the same subject matter is due within 30 days after that disclosure. In practice a scheduling order supplies different dates, and the order governs.

Thirty days is short for this discipline. Rebutting a search opinion properly means re-running the other side's analysis: obtaining their data, understanding their filters and date ranges, and reproducing their numbers before disagreeing with any of them. Where the opposing report has not disclosed enough under item (ii) to make that possible, establish it early, because the remedy takes time the rebuttal window does not contain.

One closing point. Once served, the report is the fixed statement of the opinions, and everything the expert says afterward is measured against it. Rule 26(b)(4)(A) provides that where a report is required, the deposition may be conducted only after the report is provided — the sequence is deliberate. Write it as though someone is reading it for the seam, because that reader exists and is paid to find one.

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Published 2026-08-11