What is the test for declaring a mistrial when the jury is deadlocked?

A trial judge's decision whether to declare a mistrial when he considers that the jury is deadlocked is accorded great deference, because the trial judge is in the best position to evaluate the relevant facts. See Arizona v. Washington, 434 U.S. 497, 510 (1978); United States v. Cawley, 630 F.2d 1345, 1348 (9th Cir.1980). If the jury states that it cannot agree, the judge is required to question the jury to determine whether the deadlock could be overcome by further deliberations. Cawley, 630 F.2d at 1349.