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Classification systems: DSM and ICD

Edexcel IAL Psychology · WPS04 Clinical Psychology and Psychological Skills

Diagnosis uses classification systems: agreed lists of disorders with criteria. Spec 8.1.2 names the ICD (ICD-10, and ICD-11) and the DSM (DSM-IV-TR and DSM-5). You should compare them and explain how they are used.

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What a classification system does

A classification system groups symptoms into named disorders, each with diagnostic criteria: which symptoms, how many, for how long, and what must be ruled out.

This helps clinicians to:

agree on a diagnosis (reliability)
choose treatment and predict outcome (validity)
communicate and carry out research using the same definitions.

DSM and ICD compared

	DSM	ICD
Full name	Diagnostic and Statistical Manual of Mental Disorders	International Classification of Diseases
Published by	American Psychiatric Association	World Health Organization
Coverage	Mental disorders only	All health conditions; mental disorders are one chapter
Editions in the spec	DSM-IV-TR (2000) and DSM-5 (2013); a text revision, DSM-5-TR, followed	ICD-10, and ICD-11 (adopted 2019, in effect from 1 January 2022)
Main users	USA and research worldwide	Used internationally, including UK health services

How criteria have changed

The component guide asks you to know how criteria change over time. Examples from DSM-IV-TR to DSM-5:

Schizophrenia: the subtypes (paranoid, disorganised, catatonic, undifferentiated) were dropped because they were unreliable and poorly supported.
Major depressive disorder: the bereavement exclusion was removed.
Anorexia nervosa: amenorrhoea (absence of periods) is no longer required.

ICD-11 brought ICD closer to DSM-5, for example in describing schizophrenia by symptom dimensions rather than subtypes.

Using them in practice

A clinician gathers information (clinical interview, history, observation, sometimes rating scales) and checks it against the criteria. Both systems require symptoms to cause distress or impairment and to not be better explained by a substance or medical condition.

Comparing them: DSM criteria are often more precise (exact numbers of symptoms), which can improve reliability; ICD is free to use worldwide and designed for international use, which may make it more culturally applicable.

Worked example

Explain why DSM-5 dropped the subtypes of schizophrenia.

Different clinicians often gave the same patient different subtypes, so subtypes were unreliable.
Patients' symptoms changed over time, so a subtype did not predict course or treatment well (weak validity).
DSM-5 replaced them with ratings of the severity of core symptoms.

Answer: The subtypes were unreliable and poorly supported, so DSM-5 rates symptom severity instead.

Key idea: DSM (American Psychiatric Association; DSM-IV-TR 2000, DSM-5 2013) and ICD (WHO; ICD-10, ICD-11 in effect 2022) list disorders with criteria. Compare publisher, scope, precision and international use, and know how criteria have changed.

Check yourself

Who publishes the ICD?
- The American Psychiatric Association
- The British Psychological Society
- The World Health Organization
- The Health and Care Professions Council
Show answer
The World Health Organization. ICD is published by the WHO.
How does the scope of ICD differ from that of DSM?
- ICD covers all health conditions, DSM covers mental disorders only
- DSM covers all health conditions, ICD covers mental disorders only
- ICD has no diagnostic criteria
- DSM is only used in Europe
Show answer
ICD covers all health conditions, DSM covers mental disorders only. ICD classifies all diseases; DSM is only for mental disorders.
In which year did ICD-11 come into effect?
Show answer
2022. ICD-11 was adopted in 2019 and came into effect on 1 January 2022.
Which change was made to anorexia nervosa from DSM-IV-TR to DSM-5?
- A BMI over 25 is now required
- Amenorrhoea is no longer required
- It was moved into the schizophrenia chapter
- The fear of weight gain criterion was removed
Show answer
Amenorrhoea is no longer required. DSM-5 removed the amenorrhoea criterion, partly because it excluded males and some females.
When was DSM-5 published?
- 2000
- 1973
- 2022
- 2013
Show answer
2013. DSM-5 was published in 2013; DSM-IV-TR in 2000.
Explain one reason why classification systems are useful to clinicians.
Show answer
They give standard criteria, so different clinicians are more likely to give the same diagnosis to the same patient, which improves reliability and helps choose the right treatment.. Standard criteria improve agreement, communication and treatment choice.

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Last updated 8 November 2026. Spotted a mistake? Tell us.