California, United States of America
The following excerpt is from Continental Airlines, Inc. v. McDonnell Douglas Corp., 216 Cal.App.3d 388, 264 Cal.Rptr. 779 (Cal. App. 1989):
In other words, as relevant here, while an expert may rely on inadmissible hearsay in forming his or her opinion (see People v. Coleman, supra, 38 Cal.3d at p. 90, 211 Cal.Rptr. 102, 695 P.2d 189), and may state on direct examination the matters on which he or she relied, the expert may not testify as to the details of those matters if they are otherwise inadmissible (id. at p. 92, 211 Cal.Rptr. 102, 695 P.2d 189).