Lay Witness Testimony in California

A lay witness may testify to an opinion when it is rationally based on the perception of the witness and is helpful to a clear understanding of the witness's testimony. (Evid. Code, 800.) "Generally, a lay witness may not give an opinion about another's state of mind. However, a witness may testify about objective behavior and describe behavior as being consistent with a state of mind." (People v. Chatman (2006) 38 Cal.4th 344, 397.) This is so even if the testimony touches on the ultimate issue in a case, "but only where 'helpful to a clear understanding of the testimony' citation, i.e., where the concrete observations on which the opinion is based cannot otherwise be conveyed. .'" (People v. Melton (1988) 44 Cal.3d 713, 744.) Admission of lay opinion testimony is within the trial court's discretion. (People v. Mixon (1982) 129 Cal.App.3d 118, 127.)