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Classification and Diagnosis of OCD

Most forms of mental disorder are categorised into groups according to their common symptoms, in diagnostic manuals like the Diagnostic and Statistical Manual of Mental Disorders (DSM). The DSM is produced in the USA and used in the UK; the most recent version is the DSM-IV-TR.

The Characteristics of OCD

The main characteristic is anxiety, which can arise from obsessions and compulsions.

·         Obsessions – recurrent, intrusive thoughts or impulses that are perceived as inappropriate. These cause anxiety because their content is unlike the thoughts the person usually has. Obsessions are perceived as uncontrollable, and the sufferer fears they will act on them. Common themes are ideas (germs everywhere), doubts, impulses (to shout out obscenities) or images.

·         Compulsions – repetitive behaviours or mental acts that reduce anxiety or prevent something bad from happening. Includes overt behaviours, like hand washing or checking, and mental acts, like counting or praying. Most OCD sufferers recognise their compulsions as unreasonable, but believe something bad will happen if they don’t perform that behaviour. These can also create anxiety.

Diagnostic Criteria

A clinical diagnosis is only given if there can be no other physiological cause or if the symptoms can be better accounted for by another disorder. The OCD sufferer recognises that their behaviour is unreasonable, otherwise they could have schizophrenia. A diagnosis is given if:

1.       A person has persistent thoughts etc that are experienced as intrusive and inappropriate and they cause anxiety, and they are not excessive worries about real life problems

2.      A person displays repetitive behaviours or mental acts in response to an obsession. They are not connected in any realistic way to what they are designed to prevent, they are excessive.

3.      The person recognises that these obsessions or compulsions are excessive or unreasonable.


This is the consistency of a measuring instrument. It can be measured in terms of whether two independent assessors give similar scores (inter-rater reliability measures external reliability) or whether the test items are consistent (internal reliability).

Goodman devised the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) – It is a semi structured interview used to assess symptom severity and also to monitor response to treatment. The first two sections ask patients to identify obsessions or compulsions that have been experienced now or in the past; and the third section has 10 questions which ask about the extent to which these obsessions and compulsions interfere with everyday life.

This scale has good reliability; Woody assessed 54 patients with it and found good internal consistency. Inter-rater reliability was good but test-retest results after an average of 48.5 days were bad. Kim found good test-retest reliability after two weeks. Self report and computerised versions of Y-BOCS appear to have similar reliability to interviewer administered versions. Scahill has found good reliability for the children’s version of the scale (CY-BOCS).


The extent to which a classification system, like the DSM, measures what it claims to measure.

Discriminant validity – the ability of



A substantial amount of information for OCD, thanks Abbey!

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