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UKCRC Health Research Classification System

Disputed aetiology and other

Main inclusion criteria

Conditions of unknown or disputed aetiology (such as chronic fatigue syndrome/myalgic encephalomyelitis), or research that is not of Generic Health Relevance and not applicable to the top 19 health categories with specific pathological / physiological determinants.

Advice on health categories

The Disputed Aetiology and Other category is rarely used and should only be used in specific circumstances that cannot be attributed to any of the 19 named health categories or Generic Health Relevance. There are three such circumstances suggested here. Research that does not fall into the preceding 20 health categories or these specified uses of Other should be considered outside of scope for HRCS coding.

(1) Unknown or disputed Aetiology
The most frequent circumstance where coding to Other is appropriate are conditions of unknown or disputed aetiology. Conditions include:

  • Chronic Fatigue Syndrome / Myalgic Encephalopathy / Post-Viral Fatigue Syndrome / Chronic Fatigue Immune Dysfunction Syndrome:   It is not known how these conditions are triggered; some experts have suggested they are a result of a virus but this does not explain why symptoms get worse after the virus has resolved. The aetiology of the condition has not been agreed.
  • Gulf war syndrome/illness:   This is a multi-symptom disorder affecting returning military personnel and civilians from the Gulf war. The condition has long lasting symptoms and has been recognised by the Department of Defence but there is not agreement on the underlying cause or a formal definition of the condition. Note this is a separate condition distinct from Post-traumatic Stress Disorder (PTSD, which should be coded as Mental Health).


(2) Animal Welfare
In general studies of animal welfare should be assigned the Other category. This applies to studies with direct focus on laboratory animals and the use of animals in human health research. The wider field of veterinary research is outside the scope of HRCS.

See the guidance topic on Animal Welfare for further details.

(3) Social Services Research
Not all social services research will be within scope of HRCS. Only social services research with a health relevant component should be classified, and most health-relevant social research will be applicable to the general population and therefore classified under Generic Health Relevance.

However Other also includes some types of social services research focuses on specific ‘healthy’ at risk groups that is not of relevance to the general population. Examples of such research include:

  • Research into services for young people at risk of domestic violence.
  • Research into services for minorities at risk of hate crime.


Official terminology

Full name

Short Name Unique ID
Disputed aetiology and other Other



Related external links

International Classification of Diseases (ICD 10 v2016) – Chapter XVIII:   Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R99)