Diagnosis of Mental Disorders


The 4 D's of Diagnosis

  • Deviance: The extent to which behaviour is 'rare' within society. If rare enough, could suggest a clinical disorder is present.
  • Distress: The extent to which the behaviour is causing upset to the individual.
  • Danger: How much of a danger the individual is to themselves or to other people.
  • Dysfunction: The individual's ability to cope with everday life.
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  • Evidence: Davis found people with a mental illness have a 25% increased chance of dying from unnatural causes. This supports the idea that danger is a suitable factor for diagnosis of mental illness. On the other hand, while dysfunction, deviance, distress and danger may be associated with mental illness, evidence of the 4 D's is not necessarily proof of mental illness and vice versa.
  • Applications: A strength of the 4 D's. It is useful for initial assessment and can be applied to Diagnostic manuals to determine severity (especially danger and distress). Also useful to service providers in determining need, and to non-specialised practitioners, such as GPs, for referal to mental health professionals.
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  • Strengths: Disorders such as anorexia use the concept of deviance in the diagnostic criteria (e.g 85% of expected BMI). Similarly, the cut-off used for defining learning disability is typically an IQ of 70 or below. Danger to themself or others is often used for the purposes of sectioning people who pose a significant threat.
  • Weaknesses: Some may experience some or all of the 4D's but not suffer from a mental illness e.g recently bereaved. You may be statistically/socially deviant but not mentally ill. Not all mental illesses are associated with distress. Anxiety/depression, for example, may not impact the individual's ability to function. The 4D's are highly subjective.
  • Alternative Theories: Classification systems such as DSM are generally preferred by clinicians to determine mental illness. These use criteria based on symptoms to determine mental illness.
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  • Diagnostic Statistical Manual of mental disorders (DSM)
  • It is published by the American Psychiatric Association
  • It was updated in 2015 to DSM-5
  • It was created to harmonise with ICD-10
  • There are now 3 sections:

Section 1: Explains how the DSM is organised and introduces the change.

Section 2: Lists diagnostic criteria and codes for disorders.

Section 3: Contains emerging models and measures e.g this includes categories that require more research before going into section 2. Contains disorders such as Internet Gaming Disorder which is not yet assumed to be a mental illness for Section 2.

  • Only contains diagnostic criteria for mental illnesses. 
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  • We are currently on ICD-10
  • It is devised by the World Health Organisation
  • Not just for mental disorders but all illnesses
  • Contains a section (F) for mental health disorders
  • Like the DSM, it considers each disorder as being part of a  family. Coded F for the section of the system followed by a digit for the family of mental health disorders. There will be a futher digit to represent the specific disorder.
  • e.g F32 is depression, where as F31 is bipolar depression.
  • Further categorisation comes at the next digit which follows a decimal point. e.g F32.0 is mild depression
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  • Both diagnose based on symptoms
  • Both cluster together disorders into families
  • DSM and ICD were created to harmonise with each other
  • Both are regularly revised to keep up with changes in social norms, and understanding and treatment of mental health problems.


  • ICD is a manual for classifying mental and physical illnesses, but DSM only classifies mental illnesses.
  • ICD is published in Europe by the World Health Organisation. It is intended to be simple and accessible to all (freely available on the internet). In contrast, DSM isn't freely available. Intended for use by mental health specialists.
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