Wis. Stat. § 805.18: Mistakes and omissions; harmless error.

(1) The court shall, in every stage of an action, disregard any error or defect in the pleadings or proceedings which shall not affect the substantial rights of the adverse party.

(2) No judgment shall be reversed or set aside or new trial granted in any action or proceeding on the ground of selection or misdirection of the jury, or the improper admission of evidence, or for error as to any matter of pleading or procedure, unless in the opinion of the court to which the application is made, after an examination of the entire action or proceeding, it shall appear that the error complained of has affected the substantial rights of the party seeking to reverse or set aside the judgment, or to secure a new trial.