In product liability class actions, general causation i.e., a product s propensity to cause alleged injuries is often a threshold issue to establish liability if general causation cannot be established, no class member s claim is viable. This concept is distinct from and precedes specific causation i.e. whether the product caused a particular injury. Because specific causation often cannot be determined in common, to certify a class action, plaintiffs may need evidence of a methodology to prove general causation.