In Lewis v. Workers' Comp. Appeals Bd. (1976) 56 Cal. App. 3d 938, the court considered whether a covered worker's arteriosclerosis, which led to his death, was aggravated by a prior industrial injury. The court upheld the Board's denial of death benefits, rejecting the surviving spouse's contention that pain from the industrial injury caused stress that in turn aggravated the worker's heart disease. In rejecting this chain of causation, the court stated that "no studies exist suggesting that pain is a cause of the stress that may aggravate heart disease." (Id. at p. 951.) Although it was "plausible" to theorize that pain causes stress, it was not a matter of scientific knowledge and therefore was nothing more than speculative opinion and commonsense generalization, which could not form the basis for a determination that work-related injuries contributed to the worker's death. (Id. at p. 952.)