that to one individual. As I previously testified ... I don’t know that you can, in one individual, give an assignment as to what the risk factor was or proportion which of the two significant risk factors was more or what percentage there was. BY MR. MCDAVID:
Q All you can say is that asbestos and cigarette smoking were each greater than zero percent and less than 100 percent responsible; is that right?
A Each factor — this patient[’]s lung cancer, which was the cause of his death, was caused to a substantial degree by asbestos exposure and tobacco consumption.
Q Well, would you agree with me that each factor must have been more than zero and less than 100 percent?
A Yeah, I guess I would agree with that.
Q Can you tell us anything other than that about the percentage?
A I don’t believe that, speaking on one individual, and narrowing those statistics down to one person, that I could.
The defense put on its own expert, Dr. William Weiss, also a specialist in pulmonary medicine.7 Dr. Weiss testified that asbestos exposure “did not cause [Mr. Bor-man’s] lung cancer.” On the contrary, he said only smoking “caused the lung cancer in Mr. Borman’s case.” Dr. Weiss was not asked to apportion damages.
A.
The parties agree that Pennsylvania law applies on the apportionment of damages. Before looking at specific Pennsylvania law, however, some background is appropriate. Certain types of harm “are normally incapable of any logical, reasonable, or practical division.” Restatement (Second) of Torts § 433A comment i (1965). Such harms include death, a broken limb and any single wound. Id. “By far the greater number of personal injuries ... are ... normally single and indivisible.” Id. In this case, although Mr. Borman suffered numerous diseases, his disability is the sole harm for which recovery is sought. Martin v. Johns-Manville Corp., 349 Pa.Super. 46, 56, 502 A.2d 1264, 1269 (1985) (Martin I) (“While it is apparent from the testimony at trial that appellant suffered separate harms — chronic bronchitis, emphysema and asbestosis — the ‘harm’ for which he sued and as to which the jury found him entitled to recover was his disability”), rev’d on other grounds sub nom. Martin v. Owens-Corning Fiberglas Corp., 515 Pa. 377, 528 A.2d 947 (1987) (Martin II).
While a single harm may resist apportionment, apportionment can nonetheless be invoked when the particular contribution of multiple causes can be determined on a factual basis. Restatement (Second) of Torts § 433A. The procedure remains equally viable when the plaintiff’s conduct, even if innocent, was a substantial cause of his harm. Id. comment a. In both cases, apportionment promotes fairness by “limiting] a defendant’s liability to that part of the harm of which that defendant’s conduct has been a cause in fact.” See Prosser and Keeton on Torts § 52, at 345 (5th ed. 1984). Apportionment can be harsh to the plaintiff, however, because it shifts to him “the risk of financial irresponsibility of each wrongdoer.” Id. at 351.
B.
A federal court exercising diversity jurisdiction must apply state law as declared by the highest state court. See Erie R.R. v. Tompkins, 304 U.S. 64, 71-80, 58 S.Ct. 817, 818-23, 82 L.Ed. 1188 (1938); Gruber v. Owens-Illinois Inc., 899 F.2d 1366, 1369 (3d Cir.1990). When the state’s highest court has not addressed the issue, the federal court must predict its holding. See Commissioner of Internal Revenue v. Estate of Bosch, 387 U.S. 456, 465, 87 S.Ct. 1776, 1782, 18 L.Ed.2d 886 (1967); Gruber, 899 F.2d at 1369-70. As we shall see, resolution of this matter is somewhat complicated because the Pennsylvania Supreme
7
The defense also presented the videotaped deposition of a radiologist, Dr. Joseph Becker, but neither party has relied on his testimony.