What is the test for a judge to recuse himself from hearing a motion where there is no reasonable factual basis for recusal?

The applicable recusal statute, 28 U.S.C. 455, provides that "[a]ny justice, judge, or magistrate judge of the United States shall disqualify himself in any proceeding in which his impartiality might reasonably be questioned." 28 U.S.C. 455(a). He shall also disqualify himself when he has "a personal bias or prejudice concerning a party...." Id. 455(b)(1). Although a judge must recuse himself in those circumstances, he must not simply recuse out of an abundance of caution when the facts do not warrant recusal. Rather, there is an equally compelling obligation not to recuse where recusal in not appropriate. See United States v. Holland, 519 F.3d 909, 912 (9th Cir. 2008) ("We are as bound to recuse ourselves when the law and facts require as we are to hear cases when there is no reasonable factual basis for recusal.").