Dingley v Chief Constable of Strathclyde Police

In a civil case involving disputed scientific evidence, the court must decide whether causation is established on the balance of probabilities. It must not substitute the more exacting standard by which scientists establish or disprove a hypothesis. Expert evidence remains evidence for judicial evaluation.

A temporal association and a general possibility of causation do not establish causation in the individual case. The evidence must support the inference that the relevant event was of a kind capable of producing the alleged effect and probably did so.

A police officer suffered a whiplash injury in a road accident and developed symptoms of multiple sclerosis 17 days later. Liability for the accident was admitted. The disputed issue was whether the injury had triggered the onset of symptomatic multiple sclerosis.

The Lord Ordinary accepted the claim and awarded £547,250, but gave no detailed analysis of the conflicting expert evidence. The First Division unanimously allowed the Chief Constable's reclaiming motion and reduced the award to £1,500: 1998 S.C. 548.

The officer appealed. The questions were whether trauma could trigger symptomatic multiple sclerosis in a susceptible person and, if so, whether the particular whiplash injury had done so.

1. Appeal dismissed unanimously. Lord Hope of Craighead delivered the sole substantive speech. Lord Browne-Wilkinson, Lord Nicholls of Birkenhead, Lord Steyn and Lord Clyde agreed with his reasons.

2. Per Lord Hope, a judge considering disputed scientific evidence must distinguish the civil standard of proof from the standard employed by scientists. A civil fact is proved when it is more probable than not, even by a narrow margin. The judge must assimilate the evidence, penetrate the experts' arguments and determine where the balance lies. Experts, however eminent, provide evidence and cannot replace the judgment of the court.

3. The Lord President had recognised that distinction and had not applied an impermissibly demanding standard. His rigorous testing of the clinical evidence against the epidemiological studies, animal experiments and scientific papers did not show that he had required scientific proof. His analysis disclosed no misunderstanding or material error.

4. Per Lord Hope, the epidemiological studies could be accepted for what they were worth because their calculations had not been shown by contrary evidence to be unsatisfactory. Their limitations affected the weight and use of the material. They did not establish the suggested causal relationship and required careful scrutiny of the proposed biological mechanism.

5. The fact that trauma preceded the onset of symptoms did not exclude coincidence. The animal experiments and other studies did not supply a sufficient explanation linking an ordinary whiplash injury with the development of symptomatic multiple sclerosis. Oppenheimer's study concerned principally chronic mechanical stress and did not establish that the appellant's type of injury probably caused the necessary breach of the blood-brain barrier.

6. It was insufficient to show merely that trauma in general might trigger multiple sclerosis. The evidence had to justify an inference that the particular whiplash injury damaged the relevant nerve pathways and triggered the symptoms. That inference was not established on the balance of probabilities. The First Division had therefore reached a decision which was open to it on the evidence.

1. House of Lords: The appeal was dismissed unanimously. The First Division's interlocutor was affirmed: [2000] UKHL 14.
2. First Division of the Court of Session: The reclaiming motion was allowed unanimously. The damages award was reduced to £1,500, representing the agreed solatium for the accident injuries: 1998 S.C. 548.
3. Lord Ordinary: Lord Dawson found for the appellant and awarded damages of £547,250. His opinion summarised the evidence but did not explain his evaluation of the competing expert testimony.