What is the test for a jury to determine whether negligence played any part in the injury or death of a plaintiff?

is simply whether the proofs justify with reason the conclusion that employer negligence played any part, even the slightest, in producing the injury or death for which damages are sought. It does not matter that, from the evidence, the jury may also with reason, on grounds of probability, attribute the result to other causes.... Judicial appraisal of the proofs to determine whether a jury question is presented is narrowly limited to the single inquiry whether, with reason, the conclusion may be drawn that negligence of the employer played any part at all in the injury or death.

Lies, 641 F.2d at 771 (quoting Rogers v. Missouri Pac. R.R., 352 U.S. 500, 506-07 (1957).