Wilsher v Essex Area Health Authority is a leading English tort law decision that examines the rules of causation in negligence, particularly in situations where multiple potential causes of harm exist. The case is especially important for its treatment of the “material increase of risk” test and for clarifying the claimant’s burden of proof when medical evidence cannot conclusively identify the cause of injury.
Background and Facts of Wilsher v Essex Area Health Authority
In Wilsher v Essex Area Health Authority, the claimant was a prematurely born infant who received post‑natal medical care at a hospital managed by the defendant health authority. During this period, a junior doctor negligently administered excessive oxygen to the infant. This error occurred due to the doctor’s inexperience, but the hospital accepted responsibility for the acts of its staff.
Subsequently, the child developed a serious retinal condition that resulted in blindness. Medical evidence presented in the case identified five possible causes for the injury. Four of these causes were associated with complications arising naturally from premature birth, while the fifth was the excessive oxygen administered by the junior doctor. Importantly, the evidence did not establish that any one of these factors was more likely than the others to have caused the blindness.
On the ordinary “balance of probabilities” test used in negligence cases, the claimant was unable to prove that the hospital’s negligence was the most likely cause of the injury. As a result, the question arose as to whether an alternative approach to causation could apply.
Procedural History
At first instance, the hospital was found liable for the child’s injuries. The court relied heavily on McGhee v National Coal Board, interpreting it as authority for the proposition that where multiple possible causes exist, the burden of disproving causation shifts to the defendant. On this reasoning, since the hospital had breached its duty of care and increased the risk of harm, liability was imposed.
The Court of Appeal upheld this approach. It applied the “material increase of risk” test, holding that because the hospital’s negligence had increased the risk of the type of injury suffered, and the injury fell within that risk, causation was satisfied even though the precise cause could not be identified. This interpretation effectively relaxed the traditional requirement for the claimant to prove causation.
The case was then appealed to the House of Lords.
Issues Before the House of Lords
The House of Lords in Wilsher v Essex Area Health Authority considered several interconnected legal issues:
- Whether a defendant could be held liable where medical evidence showed several possible causes of injury, but none could be identified as the probable cause.
- Whether the “material increase of risk” test could be used as a substitute for proof of actual causation.
- Whether McGhee v National Coal Board had created a new rule of law shifting the burden of proof onto defendants.
- Whether a junior doctor should be held to the same professional standard as a fully qualified doctor.
Wilsher v Essex Area Health Authority Judgement
The House of Lords allowed the appeal and dismissed the claim. In Wilsher v Essex Area Health Authority, the Lords held that it was impossible to say that the hospital’s negligence had caused or materially contributed to the child’s injury. Since the claimant could not establish causation on the balance of probabilities, liability could not be imposed.
The court rejected the interpretation of McGhee adopted by the lower courts. It clarified that McGhee did not introduce a new legal rule allowing causation to be established solely by showing an increased risk. Instead, McGhee was explained as a case where the court had drawn a robust inference of fact on the evidence available.
As a result, the House of Lords reaffirmed that, even where multiple possible causes exist, the burden of proving causation remains with the claimant.
Standard of Care and Junior Doctors
Although the claim failed on causation, Wilsher v Essex Area Health Authority confirmed an important point regarding professional standards. The House of Lords stated that junior doctors owe the same duty of care as fully qualified doctors. Inexperience does not reduce the standard expected, and hospitals may be held vicariously liable for negligent acts committed by junior medical staff.
This aspect of the decision clarified that liability in medical negligence does not depend on the seniority of the practitioner, but on whether the accepted professional standard of care has been met.
Material Increase of Risk
A central issue in Wilsher v Essex Area Health Authority was whether increasing the risk of harm could itself satisfy the requirement of causation. The House of Lords rejected this approach in cases where multiple distinct potential causes exist and only one involves negligence.
The court distinguished such situations from cases like McGhee, where there was a single causal agent and uncertainty related to the mechanism rather than the source of harm. In Wilsher, each potential cause was independent, and it could not be inferred that the negligent factor had made a material contribution to the injury.
The House of Lords therefore concluded that a mere increase in risk is not enough to establish causation in negligence where several competing causes are present.
Minority View in the Court of Appeal
In the Court of Appeal, Mustill LJ expressed a minority opinion. He argued that if a defendant’s conduct materially increases the risk of a particular injury, and that injury occurs, the defendant should be treated as having caused the injury, even if the precise extent of contribution cannot be determined.
However, this reasoning was not accepted by the House of Lords. The rejection of this approach in Wilsher v Essex Area Health Authority reaffirmed the traditional causation framework and limited the application of risk‑based reasoning.
Conclusion
Wilsher v Essex Area Health Authority is a foundational authority on causation in negligence, particularly in complex medical cases. It firmly restricts the use of the “material increase of risk” test and reasserts the principle that claimants must prove causation, even where scientific uncertainty exists. The case continues to influence how English courts approach evidential uncertainty while balancing fairness to both claimants and defendants.