Appeal

In general. A determination on appeal that there was error at trial does not always require reversal. Rather, because minor errors are common and "[a] defendant is entitled to a fair trial but not a perfect one" (Lutwak v. United States, 344 U.S. 604, 619 (1953)), every jurisdiction follows some variant of the rule that harmless errors may be disregarded.

There is no agreement, however, as to just how the harmless-error standard should be formulated or how demanding it should be. On the first question, the most common approaches are (1) an "outcome-impact" approach, which focuses on whether the error influenced the jury in reaching its verdict; and (2) the "correct result" approach, which focuses on the force of the evidence against the defendant, error aside. The latter approach has often been criticized, on the grounds that it transforms the appellate court into a trier of fact and that even guilty defendants have a right to a fair trial, but it has not disappeared from the case law (Edwards, pp. 1192–1194). The decisions do not, however, always clearly apply a well-defined approach, often adverting to a range of factors in reaching a conclusion without specifying clearly the nature of the harmless error analysis. In any event, the verbal formulas may matter less than the attitude brought to the harmless error inquiry by the appellate judges. No doubt, the stronger the appellate court's belief that the defendant was guilty, the more likely it is that the error will be found harmless; indeed, concern has been expressed that appellate courts too readily find serious errors to be harmless when convinced of the defendant's guilt (Edwards, pp. 1191–1192).

States also vary in how strong a showing of harmlessness must be made. In the federal system, reversal is required if the appellate court determines that the error "had substantial and injurious effect or influence in determining the jury's verdict" (Kotteakos v. United States, 328 U.S. 750, 776 (1946)). In the states, standards range from demanding that the defendant prove it more probable than not that an error affected the outcome (People v. Lukity, 596 N.W.2d 607, 612 (Mich. 1999)) to requiring that the prosecution establish that an error was harmless "beyond a reasonable doubt" (Commonwealth v. Story, 383 A.2d 155, 162 (Pa. 1978)).

Errors involving constitutional rights. When the error is one of federal constitutional law, the question whether the error was harmless is governed by a federal standard. In Chapman v. California, 386 U.S. 18, 24 (1967), the Court, rejecting the view that federal constitutional error is never harmless, ruled that such error required reversal unless the prosecution could demonstrate that it "was harmless beyond a reasonable doubt." The basis for imposing this requirement on state courts is uncertain: it is unclear why a state should not be free to adopt a harmless error standard on appeal that is less favorable to the defendant than the Chapman standard, when the Supreme Court has insisted that the state could eliminate appeals by the defendant altogether (Meltzer, p. 12).

While some have viewed the Chapman test as too strict, contending that an appellate court can rarely find the requisite degree of certainty that the error had no effect (Traynor, pp. 43–44), others have contended that by its nature the test may not be strict enough, for constitutional error (such as the admission of impermissible evidence) may have significantly shaped trial strategies in ways not apparent to the appellate court (Saltzburg, p. 990).

The Supreme Court has stressed that constitutional errors are presumptively subject to harmless error analysis (Rose v. Clark, 478 U.S. 570, 579 (1986))—even, for example, admission of a coerced confession (Arizona v. Fulminante, 499 U.S. 279, 285 (1991)), or the failure to instruct the jury of the need to find an essential element of the offense (Neder v. United States, 119 S. Ct. 1827, 1831 (1999)). The Court has, however, recognized a limited class of fundamental constitutional errors—including total deprivation of the right of counsel, denial of the right to self-representation, trial before a biased judge, racial discrimination in selection of the grand jury, denial of the right to a public trial, and improper instructions on proof beyond a reasonable doubt—that are "so intrinsically harmful" and that so infect the entire trial process that they defy harmless error analysis and require automatic reversal (Neder v. United States, p. 1833).