In every personal injury case, it is necessary to establish proof of the cause and effect relationship between an accident and the plaintiff's claimed injuries. Of course, the burden of such proof rests with the plaintiff. The advances in science and technology in the past years have produced tools to facilitate a more objective assessment of the causation issue in litigation. For example, given the advent of MRI and CT technologies, a radiologist can distinguish between signs of acute trauma and chronic, pre-existing degenerative conditions. Moreover, the development of biomechanical engineering has provided the basis for a scientific analysis of causation in appropriate cases.

In New York, the task of proving the essential element of causation ordinarily falls to the plaintiff's doctor in personal injury trials. This doctor's testimony advises that the accident was “the competent producing cause of the injury.” Usually this causal connection is stated with “a reasonable degree of medical certainty.” However, the doctor's “certainty” of the causal link may often be based on incomplete data or subjective beliefs that are not necessarily supported by an objective analysis of the circumstances of the accident. Medical experts routinely base their opinions of the causal nexus between the accident and injury solely on the plaintiff's subjective verbal description of the event, usually provided at the initial visit.

“Reliability” is the chief criterion for admissibility of a doctor's testimony on causation in New York. As we'll discuss ahead, biomechanical engineering calls into question the reliability of medical testimony on this essential element of the personal injury lawsuit.