McTear v Imperial Tobacco: understanding the role and limitations of expert epidemiological evidence in scientific litigation.

The use of epidemiological evidence in litigation presents a range of challenges for both litigants and the courts. Given the complex statistical basis of epidemiology itself, it is possible that the technical and factual constraints associated with such evidence may fail to be properly considered by a trier of fact. The recent Scottish decision in McTear v Imperial Tobacco Ltd [2005] Scots CSOH 69 sets a high standard for the future use of epidemiological evidence and thoroughly evaluates the strengths and weaknesses of epidemiology generally. While epidemiological evidence remains controversial, and cannot in itself prove direct causation (nor causation in the individual), it is likely it will continue to be adduced as indirect evidence of general causation. It is also likely, however, that both the subjective and objective processes involved in epidemiological study design and reporting will be questioned by courts more thoroughly than has historically been the case. Further, failure by a party to adduce primary evidence (ie original data sets and interpretation thereof) of an epidemiological study which it seeks to rely on at trial will most likely undermine the value of adducing such evidence in the first place.