Is a judge required to recuse himself from hearing cases?

A judge shall recuse himself "in any proceeding in which his impartiality might reasonably be questioned." 28 U.S.C. 455(a). "[T]he trial judge is required to recuse himself only when a reasonable person with knowledge of all the facts would conclude that the judge's impartiality might reasonably be questioned," United States v. Winston, 613 F.2d 221, 222 (9th Cir.1980), and "must hear cases unless some reasonable factual basis to doubt the impartiality or fairness of the tribunal is shown by some kind of probative evidence," Blizard v. Frechette, 601 F.2d 1217, 1221 (1st Cir.1979).