What is the test for a jury to overturn a finding in a civil case?

^3. The rationale for this rule is the protection of jury verdicts which "can be attacked and set aside on the testimony of those who took part in their publication and all verdicts could be, and many would be, followed by an inquiry in the hope of discovering something which might invalidate the finding. Jurors would be harassed and beset by the defeated party in an effort to secure from them evidence of facts which might establish misconduct sufficient to set aside a verdict." Tanner v. United States, 483 U.S. 107, 119-20 (1987) (citations omitted).