What is the test for a juror's conduct in a civil case?

"[N]ot every incident involving a juror's conduct requires or warrants further investigation. `The decision whether to investigate the possibility of juror bias, incompetence, or misconductlike the ultimate decision to retain or discharge a jurorrests within the sound discretion of the trial court. [Citation.] . . . [] As our cases make clear, a hearing is required only where the court possesses information which, if proven to be true, would constitute "good cause" to doubt a juror's ability to perform his duties and would justify his removal from the case. [Citation.]' [Citation.]" (People v. Cleveland (2001) 25 Cal.4th 466, 478.)