What is the test for admissible evidence of "likely to have influenced the verdict improperly" in a civil case?

⁴ Evidence Code section 1150, subdivision (a), states that evidence of "statements made, or conduct, conditions, or events occurring" that are "likely to have influenced the verdict improperly" are admissible, but "[n]o evidence is admissible to show the effect of such statement, conduct, condition, or event upon a juror either in influencing him to assent to or dissent from the verdict or concerning the mental processes by which it was determined." This means that evidence of " "overt acts, objectively ascertainable" " is admissible, but evidence of " "the subjective reasoning processes of the individual juror, which can be neither corroborated nor disproved," " is inadmissible. (People v. Collins (2010) 49 Cal.4th 175, 249, 110 Cal.Rptr.3d 384, 232 P.3d 32.)