The Expert’s Role in Causation: Distinguishing Negligence from Abuse

The Medico-Legal Distinction

In medico-legal practice, distinguishing between negligence—specifically systemic failure or professional oversight—and intentional abuse is frequently central to liability and causation. This distinction determines the legal pathway for a claim, often dictating whether an action is framed within clinical or institutional negligence or under the rubric of intentional harm. Establishing the causal link requires a methodology that rigorously isolates the specific nature of the harm from the claimant’s underlying clinical or developmental trajectory.

The Clinical Framework: Distinguishing Pathologies

From a psychiatric perspective, the injury profile presented by a survivor often reflects a complex intersection of factors. Under the ICD-11, complex post-traumatic stress disorder (CPTSD) incorporates both the core symptoms of PTSD and disturbances in self-organisation. An expert witness must determine the extent to which these symptoms arise from an acute event of abuse versus the cumulative impact of chronic neglect or systemic failure.

Paediatric assessments often focus on non-accidental injury (NAI) indicators, comparing clinical presentations against developmental expectations. Where the allegation involves systemic failure within a care setting, the expert must assess whether the developmental trauma or attachment disruption observed is consistent with a specific period of alleged neglect or whether it reflects wider developmental instability. In cases where claimants have been subject to trafficking and related sexual abuse, the clinical assessment must differentiate between the trauma directly attributable to the act of abuse and the psychological sequelae of institutional and statutory failure to provide safety.

Legal Relevance and the Test of Causation

The distinction between negligence and abuse informs the legal test for liability. In negligence claims, the claimant must establish a duty of care, a breach, and causation under the ‘but-for’ test. Conversely, claims involving intentional abuse may pivot on vicarious liability, as seen in Various Claimants v Barclays Bank plc [2020] UKSC 13 or Armes v Nottinghamshire County Council [2017] UKSC 60. The expert’s role is to delineate the causation of the harm, ensuring the court can accurately quantify the damage associated with the specific breach or intentional act, rather than attributing all comorbid psychiatric symptoms to a single source.

In historic abuse claims, the application of Section 33 of the Limitation Act 1980 often hinges on the expert’s ability to provide a retrospective assessment of the claimant’s ability to disclose. This requires an examination of trauma-informed concepts, such as betrayal trauma theory, which the court must weigh against the prejudice caused by the passage of time.

Methodological Considerations

A frequent challenge in proceedings is the conflation of general adverse childhood experiences (ACEs) with specific, actionable abuse or negligence. Expert methodology must be sufficiently robust to distinguish between:

• Harm directly resulting from a specific, identified act of abuse.
• Damage sustained due to a failure to prevent foreseeable harm (negligence).
• Pre-existing psychological vulnerability or developmental background.

Experts often utilise standardised psychometric tools such as the PCL-5 or the ITQ for CPTSD to assess symptomatic impact. However, these tools are supplementary to the clinical interview and record review. An expert failing to triangulate psychometric data with the longitudinal clinical history risks producing an opinion that is vulnerable to challenge during cross-examination.

Procedural Duties and Multi-Disciplinary Input

Under the Civil Procedure Rules (CPR), the expert’s overriding duty is to the court (CPR 35.3). In multi-disciplinary claims involving both physical injury and psychological sequelae, the court may require input from multiple experts. Where the court directs that evidence be given by a single joint expert under CPR 35.7, the experts are to be instructed in accordance with CPR 35.8. If separate experts are instructed, they may be directed to hold discussions and produce a joint statement under CPR 35.12 to clarify areas of agreement and disagreement. This process is essential for narrowing the issues in cases where the distinction between physical trauma and the psychological aftermath is contested.

Practical Guidance for Instructing Solicitors

Solicitors should consider the following when instructing an expert witness:

• Precision in Instructions: Explicitly request the expert to distinguish between the primary harm caused by abuse and secondary harm resulting from negligent management or institutional failure.
• Records Management: Provide a complete, chronological index of records. Experts require a granular understanding of the claimant’s developmental and clinical history to form a reliable opinion.
• Proportionality: Restrict the request to what is reasonably required to resolve the specific issues in the claim, in line with CPR 35.1.
• Independence: Recognise that the expert’s duty is to the court; the role of the instructing solicitor is to provide the evidential basis, not to shape the expert’s findings.