Johns-Mansville Sales Corp., 781 F.2d 1061, 1062-65 (5th Cir. 1986) (rejecting pro-rata liability in favor of apportioned liability based upon relative causation of dose-related diseases) Mathematical certainty is not a prerequisite to apportionment; evidence that tends to show relative proportions of damages caused by each tortfeasor, or other source, is sufficient for a jury to apportion properly. [read post]