Diaz v. United States
The court interpreted a provision of the Federal Rules of Evidence regarding the admissibility of expert witness testimony.
144 S. Ct. 1727 · No. 23-14 · 2023 term · Roberts Court
Decided Jun 20, 2024 · argued Mar 19, 2024
Criminal procedure · Extra-legal jury influences: miscellaneous
Majority opinion: Clarence Thomas
The voteMajorityDissent
6–36 in the majority, 3 in dissent
3 dissents (6–3)
Affirmed. Diaz lost.
What this ruling means
Affirmed: the Supreme Court upheld the decision of the U.S. Court of Appeals, Ninth Circuit, so it stands (sometimes with changes the Court made to it).
Diaz was the petitioner, the side that asked the Supreme Court to review the case. “Lost” means the Court did not give that side the result it asked for.
From the Supreme Court Database. A justice who agreed with the result but not the reasoning counts in the majority.
Summary
The opening of the case’s Wikipedia article: what the case was about and what the Court held.
Diaz v. United States, 602 U.S. 526 (2024), is a United States Supreme Court case. The court interpreted a provision of the Federal Rules of Evidence regarding the admissibility of expert witness testimony.
Data notes
The text is Wikipedia’s (CC BY-SA 4.0), matched to the case by its citation, docket number or name and year, and is not checked against the opinion. The site keeps the article’s opening section, ending on its last full sentence. The one-sentence summary under the title is the Decisions list’s: Wikipedia’s own ruling sentence, or, tagged “AI-written”, one Claude wrote from this opening.
How the justices voted
Each justice who took part, placed by their Martin–Quinn ideology score for the 2023 term. Filled: the 6 in the majority. Hollow: the 3 in dissent. Colour is the party of the president who appointed them.
Majority(6)
Clarence ThomasWrote the majority opinion
Ketanji JacksonWrote a concurrence
John RobertsJoined the majority
Brett KavanaughJoined the majority
Amy BarrettJoined the majority
Samuel AlitoJoined the majority
Dissent(3)
Neil GorsuchWrote a dissent
Sonia SotomayorJoined a dissent
Elena KaganJoined a dissent
Data notes
Each justice’s vote and what they wrote are from the justice-centered file of the Supreme Court Database. “Wrote a concurrence” means the justice sided with the majority and wrote separately; a justice who dissented in part is counted on the side they took overall. A justice who wrote nothing is listed as joining their side.
Positions are each justice’s Martin–Quinn score for the case’s term, the same scores as the Ideology page: negative is more liberal, positive more conservative. A score sums up a justice’s votes across the whole term, so it says where they usually sit, not why they voted as they did here. The median line is the Court’s median justice that term.
The parties
Who brought the case to the Court, who answered it, and how it got there.
- Petitioner
- DiazPerson convicted of crime
- Respondent
- United StatesUnited States
- Reached the Court by
- Certiorari (the Court chose to hear it)
Data notes
The names are the two sides of the case’s title. The description under each is the Supreme Court Database’s category for that party, in its own wording. The petitioner is the side that asked the Supreme Court to review the decision below. “Why it was taken” appears only when the majority opinion says lower courts disagreed or were unsure about the question; reasons that would fit any case (“to resolve the question presented”, “an important question”) are left out.
The law at issue
The law the Court was asked to apply, and the kind of power it used to decide.
- Provision
- Federal Rules of Evidence
- Kind of law
- Court Rules
- Decided by
- Statutory construction
Data notes
The Supreme Court Database codes the main constitutional provision, statute or court rule each case turned on, and the basis of the decision: judicial review of a federal or state law, interpreting a statute, supervising the lower courts, and so on. A case can rest on more than one. “Overruled” counts only where the majority opinion says so.
Timeline
What happened at the Court and how the case got there, newest first.
- Jun 20, 2024DecidedDecided · Decided 6–3: affirmed. Diaz lost.
- Mar 19, 2024ArguedArgued · Oral argument before the Court.
- Not datedTaken upTaken up · The Supreme Court agreed to hear the case (certiorari).
- Not datedCourt belowCourt below · Decided by the U.S. Court of Appeals, Ninth Circuit: affirmed.
- Not datedBeganBegan · The case began in the California Southern U.S. District Court.
Data notes
From the Supreme Court Database: the court the case began in, the court whose decision the Supreme Court reviewed and what that court did, how the case came to the Court, and the dates of argument and decision. The database does not date the steps in the lower courts. Court names are the database’s.
Other decisions on the same issue
10 other argued cases since 1946 on extra-legal jury influences: miscellaneous, newest first.
- Thomas L. Carey, Warden v. Mathew Musladin549 U.S. 70Dec 11, 2006 · 549 U.S. 70Criminal procedure9–0Unanimous band
- United States v. Michael E. Gaudin515 U.S. 506Jun 19, 1995 · 515 U.S. 506Criminal procedure9–0Unanimous band
- David Riggins v. Nevada504 U.S. 127May 18, 1992 · 504 U.S. 127Criminal procedure7–27–2 band
- Holbrook, Superintendent, Massachusetts Correctional Institution, et al. v. Flynn475 U.S. 560Mar 25, 1986 · 475 U.S. 560Criminal procedure9–0Unanimous band
- Chandler et al. v. Florida449 U.S. 560Jan 26, 1981 · 449 U.S. 560Criminal procedure8–0Unanimous band
- Estes v. Texas381 U.S. 532Jun 7, 1965 · 381 U.S. 532Criminal procedure5–45–4 band
- Morford v. United States339 U.S. 258Apr 10, 1950 · 339 U.S. 258Criminal procedure8–0Unanimous band
- Dennis v. United States339 U.S. 162Mar 27, 1950 · 339 U.S. 162Criminal procedure5–27–2 band
- Frazier v. United States335 U.S. 497Dec 20, 1948 · 335 U.S. 497Criminal procedure5–45–4 band
- Fay v. New York332 U.S. 261Jun 23, 1947 · 332 U.S. 261Criminal procedure5–45–4 band
Data notes
Every other orally argued case with a clear vote, from the 1946 term on, that the Supreme Court Database files under the same issue as this one. The database gives each case one issue from a list of about 270 (abortion, search and seizure of vehicles, the death penalty, and so on), whatever law it turned on.
Official record
Read the argument audio on Oyez and Wikipedia. Case data from the Supreme Court Database, Version 2026 Release 01, through the 2025 term.