California, United States of America
The following excerpt is from People v. McAlpin, 283 Cal.Rptr. 382, 53 Cal.3d 1289, 812 P.2d 563 (Cal. 1991):
12 The contrast, of course, is with opinion testimony by an expert, which may be based on information furnished to the expert by others, provided only that it is the kind of information on which experts may reasonably rely. (Evid.Code, 801, subd. (b).) As succinctly put in Manney v. Housing Authority, supra, 79 Cal.App.2d 453, 459-460, 180 P.2d 69, "For a nonexpert to be competent to give an opinion ... he must be testifying about facts that he has personally observed; but the expert ... may give his opinion, although he did not personally observe the facts, basing his opinion upon the facts testified to by other witnesses [and] put to him in the form of hypothetical questions."