Opinion of the Court
in SSA hearings. As explained above, Congress intended those proceedings to be “informal” and provided that the “strict rules of evidence, applicable in the courtroom, are not to” apply. Perales, 402 U. S., at 400; see 42 U. S. C. §405(b)(1); supra, at 2. So Biestek does not press for a “procedural rule” governing “the means through which an evidentiary record [must be] created.” Tr. of Oral Arg. 6; Reply Brief 13. Instead, he urges a “substantive rule” for “assess[ing] the quality and quantity of [record] evidence”—which would find testimony like O’Callaghan’s inadequate, when taken alone, to support an ALJ’s factfinding. Id., at 12.
And Biestek also emphasizes a limitation within that proposed rule. For the rule to kick in, the applicant must make a demand for the expert’s supporting data. See Brief for Petitioner i, 5, 18, 40, 55; Tr. of Oral Arg. 25–26. Consider two cases in which vocational experts rely on, but do not produce, nonpublic information. In the first, the applicant asks for the data; in the second, not. According to Biestek, the expert’s testimony in the first case cannot possibly clear the substantial-evidence bar; but in the second case, it may well do so, even though the administrative record is otherwise the same. And Biestek underscores that this difference in outcome has nothing to do with waiver or forfeiture: As he acknowledges, an applicant “cannot waive the substantial evidence standard.” Id., at 27. It is just that the evidentiary problem arises from the expert’s refusal of a demand, not from the data’s absence alone. In his words, the testimony “can constitute substantial evidence if unchallenged, but not if challenged.” Reply Brief 18.
To assess Biestek’s proposal, we begin with the parties’ common ground: Assuming no demand, a vocational expert’s testimony may count as substantial evidence even when unaccompanied by supporting data. Take an example. Suppose an expert has top-of-the-line credentials,
