In a personal injury action, what is the test for denying a plaintiff's right to withhold income tax information?

Defendants sought to introduce evidence that plaintiffs had filed no income tax returns for the years immediately preceding the accident. The trial court rejected that request, basing its ruling in part on section 352 of the Evidence Code. Defendants rely on Newson v. City of Oakland (1974) 37 Cal.App.3d 1050, 112 Cal.Rptr. 890. That case, however, dealt only with whether a litigant had a privilege to withhold similar information. As we have said, the ruling here was not based on that ground. We conclude that the trial court did not err in its ruling. While a jury might conclude from the failure to file a tax return that plaintiff had not earned as much prior to the accident as he here testified he had earned; on the other hand, the jury might conclude that he was a tax evader. Not to open up the case to that kind of pure speculation is the very purpose of section 352.