Expert Evidence and Causation: Assessing Material Contribution in Institutional Abuse

In abuse injury litigation, the determination of causation remains a significant challenge for legal practitioners and experts. Unlike cases involving a single, discrete injury, claims arising from institutional abuse typically involve complex, longitudinal patterns of harm. For the instructing solicitor, navigating the distinction between the ‘but-for’ test of causation and the doctrine of material contribution is essential when preparing instructions for psychiatric or psychological experts.

The Medico-Legal Framework of Causation

The standard ‘but-for’ test requires the claimant to demonstrate that, but for the defendant’s breach of duty, the injury would not have occurred. However, in institutional settings where multiple stressors may interact, evidence often reveals a constellation of psychological injuries that cannot be easily partitioned into ’caused by the abuse’ versus ’caused by other life events’.

Expert clinicians, in their assessment of institutional abuse, must grapple with the cumulative nature of harm. When an individual suffers from complex post-traumatic stress disorder (CPTSD), the pathology is often the result of protracted interpersonal trauma. If institutional neglect has exacerbated or materially contributed to the development or maintenance of this condition, the expert must be able to delineate the threshold at which the defendant’s actions have made a material contribution to the overall psychiatric damage. Practitioners should consider how litigation responses to institutional failures inform the approach to cumulative injury in contemporary reports.

Distinguishing Contribution from But-For Causation

The application of material contribution is invoked where the conventional but-for test fails to account for the reality of indivisible harms. An expert witness is expected to provide a reasoned, evidence-based opinion on whether the institutional setting made more than a negligible contribution to the psychiatric injury sustained. This assessment requires a thorough review of the clinical history to establish a baseline of function, assessing whether, on the balance of probabilities, the clinical presentation would be less severe had the institution exercised its duty appropriately.

Clinical Methodology and Multi-Disciplinary Input

Establishing causation requires a trauma-informed methodology. Psychiatric experts must integrate historical disclosures with current clinical presentations. Where physical abuse is also alleged, the input of a paediatrician or physical medicine expert may be required to correlate documented injuries with psychological outcomes. Under the Civil Procedure Rules (CPR), the expert’s duty under CPR 35.3 is to the court, overriding any duty to the party instructing them.

• Detailed Chronology: Reconstructing the timeline of institutional placement versus symptom onset is paramount.
• Differential Diagnosis: Experts should differentiate between the effects of institutional abuse and pre-existing vulnerabilities or later life stressors.
• Symptom Validity: The use of instruments such as the SIMS or TOMM may be considered if there is a significant question regarding the consistency of reported symptoms, though these should be applied with caution in trauma contexts.
• Procedural Compliance: Reports should adhere to the requirements set out in CPR 35.10.

Common Pitfalls in Expert Reporting

A frequent error is the failure to distinguish between a clinical diagnosis and legal causation. While a psychiatrist may diagnose CPTSD, they must explain the causative mechanism by which the institutional environment caused or materially contributed to that disorder. Experts must also avoid ‘over-attribution’ and acknowledge when an injury is likely to have been sustained independently of the institutional setting.

Where two or more experts are instructed, they may be directed by the court under CPR 35.12 to engage in discussions to identify areas of disagreement. Such a joint statement should remain an independent synthesis of medical opinion. In contrast, when a court exercises its power under CPR 35.7 to appoint a single joint expert, instructions are governed by CPR 35.8, and the expert does not participate in a joint statement process with another party-appointed expert.

Practical Guidance for Instructing Solicitors

To assist the expert, solicitors should ensure that instruction materials include the full chronology of the claimant’s contact with the institution, including any contemporaneous medical or social services records. Given that records of ‘delayed disclosure’ are common in historic abuse claims, experts should be familiar with the clinical literature regarding memory and trauma, particularly concerning why survivors may only present symptoms or seek legal redress long after the events occurred, within the parameters of the Limitation Act 1980.