What is the test for establishing that a jury was deadlocked prior to the judge's statement?

purportedly strong evidence on the issue, as "the jury was deadlocked prior to the judge's statement," which established that "necessarily, at least one of the jurors was not persuaded by the strength of the prosecution's evidence"]; Bollenbach v. U.S. (1946) 326 U.S. 607, 614 [an erroneous presumption communicated by the trial court to the jury was prejudicial despite the strength of the evidence on that issue because "for seven hours the jury was unable to find guilt . . . , but reached a verdict of guilty . . . five minutes after their inquiry was answered by an untenable legal proposition" and "[i]t would indeed be a long jump at guessing to be confident that the jury did not rely on the erroneous 'presumption' given them as a guide"].)