Those courts that have excluded the testimony of grief experts have relied on some or all of the following basic rationales: (1) The testimony is not admissible to relay "matters within the common experience of jurors." (2) The testimony is not admissible when there is a danger that the jury will give such testimony undue weight. (3) The testimony is not admissible merely to relay what the expert was told by lay witnesses. El-Meswari v. Washington Gas Light Co., 785 F.2d 483, 487 (4th Cir. 1986); Angrand v. Key, 657 So.2d 1146, 1148-50 (Fla. 1995); Robles v. Chicago Transit Authority, 527 N.E.2d 361, 367-68 (Ill.App. 1988).
Evidence of grief traditionally has been provided through the testimony of lay witnesses, as opposed to experts. Angrand, 657 So.2d at 1149 (relevant testimony usually comes from "survivors, friends, ministers, and others who testify as fact witnesses, as opposed to experts"); Robles, 527 N.E.2d at 367 ("family members" were most appropriate to testify as to their grief).
Admissible in particular cases
In limited number of cases, courts have allowed grief experts to testify, where there is a finding that such testimony might be more helpful than the testimony of the plaintiff's lay witnesses. For example, a Florida state appellate court held that the testimony was admissible when the expert was "actively involved in therapy" with the survivors and provided specific information in regard to the surviving family
Another decision, this one by the Oklahoma Supreme Court, went so far as to say that, at least for purposes of proving grief in an action by a parent for the wrongful death of a child, expert testimony may "often be useful and proper, if not absolutely necessary."
http://www.allbusiness.com/legal/litigation/1111775-1.html excellent article at link regarding admissibility of grief experts