What is the test for asserting Fifth Amendment privilege in a tax return?

We have recently considered the validity of a Fifth Amendment assertion made in a tax return to avoid self-incrimination for non-tax-law violations. United States v. Neff, 615 F.2d 1235 (9th Cir., 1980). We held that the validity of such an assertion should be assessed in light of the following factors: whether the privilege was asserted at the time of filing the return and in response to specific questions contained therein, whether the taxpayer was faced with a real and appreciable danger of self-incrimination, and whether he had reasonable cause to believe that an honest response to the questions would provide a link in the chain of evidence needed to prosecute him for a crime. Id. Moreover, we determined that the trial judge is to ascertain the potentially incriminatory nature of elicited responses by examining the questions, their setting, and the peculiarities of the case, with the burden of showing their hidden danger falling upon the taxpayer should the trial judge find the questions to be innocuous. Id., at 1240.