What is the burden of persuasion in a federal civil case?

Burden of persuasion differs critically between subsections (a) and (b). Under subsection (a), the prosecution has "the burden of showing the absence of prejudice," Olano, 507 U.S. at 741, 113 S.Ct. at 1781, and "before a federal constitutional error can be held harmless, the court must be able to declare a belief that it was harmless beyond a reasonable doubt." Chapman v. State of California, 386 U.S. 18, 24, 87 S.Ct. 824, 828, 17 L.Ed.2d 705 (1967). Subsection (b), by contrast, imposes the burden on the defendant: