LAW AND EPIDEMIOLOGICAL EVIDENCE: DOUBLE, TOIL AND TROUBLE

In Sienkiewicz v Greif (UK) Limited, the Supreme Court discussed a doubles-therisk test based on epidemiological studies for the proof of individual causation in toxic tort litigation in the United Kingdom. The issue was obiter in the Appeal. Differing views were expressed and the speeches cannot be interpreted as rejecting the test as a matteroflaw. Unsurprisingly,therefore, reference continues to be made to the test and the analogous argument that causationcan be proved by a statistical likelihood of a better outcome in the absence of breach. It is generallyaccepted that risk-based epidemiological evidence is admissible in litigation. This raises the question of the continued forensic role of such evidence in English common law. We use a case study with variationsto indicate a range of issues that may arise in the application of epidemiological evidence. The issues are multi-faceted and demonstrate why a simple formulaic rule based on doubling of the risk ('a relative risk of two') could never work. An arbitrarycut-off at a relative risk of two would lead to injustice. Whilst the epidemiological evidence is telling us something of relevance, it does not answerall the questions thatare specific to a particularcase at a particularmoment in time. A better understandingof epidemiological evidence and how it can be applied in individual cases will assist, but it is reasonable to anticipatethat considerablecontroversy will persistin clinical negligence and toxic tortlitigation. For that reason, we propose a structuredapproach to the assessment and use ofepidemiologicalevidence in litigation.This approachmay assistdecisionmakers and others as they navigate the currentmuddles and misconceptions that surround the forensic role of such evidence.