“I find it preferable to explain the process without using the term secondary or evidential burdens. It is not strictly accurate to speak of the burden shifting to the defendant when what is meant is that evidence adduced by the plaintiff may result in an inference being drawn adverse to the defendant. Whether an inference is or is not drawn is a matter of weighing evidence. The defendant runs the risk of an adverse inference in the absence of evidence to the contrary. This is sometimes referred to as imposing on the defendant a provisional or tactical burden; see Cross on Evidence, 3rd Ed, at p129. In my opinion, this is not a true burden of proof, and the use of an additional label to describe what is an ordinary step in the fact finding process is unwarranted. The legal or ultimate burden remains with the plaintiff, but in the absence of evidence to the contrary, adduced by the defendant, an inference of causation may be drawn, although positive or scientific proof of causation has not been adduced.”