What is the test for reversal of a finding that a single error in the course of a criminal trial is prejudicial?

Appellant contends that the cumulative effect of all of the instructional errors mandates reversal, even if no single error does. This contention lacks merit. "Lengthy criminal trials are rarely perfect, and this court will not reverse a judgment absent a clear showing of a miscarriage of justice. [Citations.]" (People v. Hill (1998) 17 Cal.4th 800, 844.) "Nevertheless, a series of trial errors, though independently harmless, may in some circumstances rise by accretion to the level of reversible and prejudicial error." (Ibid.) We have determined that the errors that occurred were not individually prejudicial. Given their comparative insignificance, we also conclude that they were not collectively prejudicial.