What are outliers?
The identification of statistical outliers is an important part of the National Clinical Audit and Patient Outcomes Programme (NCAPOP) and National Joint Registry (NJR) work. Both NCAPOP and NJR are hosted by HQIP. The identification of statistical outliers signals potential variation in care that can indicate differences in patient outcomes, safety, and experience.
Outliers are identified by comparing results across organisations and flagging those that are much higher or lower than the typical range of results. Identifying outliers in this way highlights unwarranted variation and provides an early warning system for hospital trusts. Those trusts can use this insight to review and change how they deliver care before issues escalate.
The national audit providers within the NCAPOP portfolio are commissioned by HQIP, and they use statistically robust processes, methods and methodologies for outlier analysis.
Details regarding the NJR processes can be found on the NJR website: The National Joint Registry – Working for patients, committed to excellence.
HQIP’s management of a consistent national outlier process supports accountability through data transparency and ensures organisations, clinicians, and patients can have confidence in the results. An outlier flag is a starting point for investigation rather than a definitive judgement. Identifying unusual performance through clinical outliers provides a robust basis for learning and improvement. Trusts can use it to understand potential gaps in clinical pathways, identify any issues in coding practices, or take the opportunity to adopt best practice from high-performing organisations. All of which helps deliver meaningful improvement for patients and the healthcare system.
Outlier definitions
| Type | Definition |
| Alert | > 2 standard deviations from expected performance |
| Alarm | > 3 standard deviations from expected performance |
| Complete non-participation in the audit | The healthcare provider is eligible for at least one metric but has not participated in the audit at all. See Appendix A: Non-participation here: NCAPOP-Outlier-Guidance_2025-Oct-Update-v2.pdf |
| Persistent outlier NOF definition: | A trust that is an alarm for a metric in the most recent four quarters and an alarm in the preceding four quarters for the same metric. |
National guidance: Outlier management guidance for HQIP-commissioned programmes
The following guidance and resources are for HQIP-commissioned audits operating in England and Wales. This guidance was last updated in November 2025.
- NCAPOP Outlier Guidance, Identification and Management of Outliers
- Summary of changes (November 2025)
- Template for use to notify CQC of outliers (July 2026) – Provides clarity for NCAPOP providers on the expected response format of fields.
- Template to record trust responses for publication (July 2026) – Provides clarity for NCAPOP providers when discharging their outlier responsibility. Enables transparency of responses between the audit provider and the trust healthcare provider.
Previous national archived guidance
For copies of earlier versions of the NCAPOP outlier guidance, please get in touch by email.
Incorporation of outliers into the National Oversight Framework (NOF)
Details can be found here: NHS England » NHS Oversight Framework 2026/27
NHS healthcare trust NOF outliers
The spreadsheet below (refreshed quarterly) provides details about trust outliers:
