What is the legal test for dismissing a juror?

If at any time, whether before or after the final submission of the case to the jury, a juror dies or becomes ill, or upon other good cause shown to the court is found to be unable to perform his or her duty, ... the court may order the juror to be discharged and draw the name of an alternate.... ( 1089.) While a trial court has broad discretion to remove a juror for cause, it should exercise that discretion with care. (People v. Barnwell (2007) 41 Cal.4th 1038, 1052, 63 Cal.Rptr.3d 82, 162 P.3d 596, fn. omitted.) The trial court's decision to dismiss a sitting juror will be upheld on review if the juror's inability to serve appears in the record as a demonstrable reality. (People v. Wilson, supra, 44 Cal.4th at p. 821, 80 Cal.Rptr.3d 211, 187 P.3d 1041.) This standard of review is more stringent than the deferential substantial evidence test.

[340 P.3d 335]

(Ibid. ) Under the demonstrable reality standard ... the reviewing court must be confident that the trial court's conclusion is manifestly supported by evidence on which the court actually relied. (People v. Barnwell, supra, at p. 1053, 63 Cal.Rptr.3d 82, 162 P.3d 596.)