Schizophrenia AQA Psychology



A severe mental illness where contact with reality and insight are impaired. 

Diagnosis and classification of schizophrenia 

Classification of schizophrenia - process of organising symptoms into categories based on which symptoms cluster together in sufferers.

  • Does not have a single defining characteristics but rather a cluster of symptoms some of which appear to be unrelated
  • Two major systems for classification of mental disorder = ICD-10 & DSM-5/V
  • These differ slightly in their classification of schizophrenia. 
  • DSM-5 — one positive symptom  ICD-10 — two or more negative symptom
  • ICD-10 also recognises a range of subtypes of schizophrenia such as paranoid schizophrenia (delusions and hallucination), catatonic schizophrenia (disturbance to movement) and Hebephrenic schizophrenia (negative symptoms). 


Additional experiences beyond those of ordinary existence, such as hallucinations. 

Hallucinations: unusual sensory experiences. Some related to environment and some not (voices heard). 

Delusions: also known as paranoia, are irrational beliefs. Common delusions include being an important historical, political or religious figure such as Jesus or Napoleon. It also involves being persecuted; by government or alien or for having super powers. Delusions can make suffer behave differently that makes sense to them and not anyone else because they believe someone else ins in control of them. 


Involves loss of usual abilities and experiences.

Avolition: (apathy) finding it difficult to begin or keep up with goal related activity (actions performed in order to achieve a result). Reduced motivation to carry on. Three sings of avolition; poor hygiene, lack of persistence in work or education and lack of energy. 

Speech poverty:  Changes in patterns of speech. It is negative symptom as it is reduction in amount and quality of speech. Now it also include speech disorganisation - change topic mid sentence (positive symptom)


  1. Reliability 

Means consistency. An important measure of reliability is inter-rater reliability, the extent to which different assessors agree on their assessment. In the case of diagnosis - the extent to which two or more mental health professionals arrive at the same diagnosis.

Psychologist has two psychiatrists independently diagnose 100 patients using both DSM and ICD criteria. Inter-rater reliability was poor, one P diagnosing 26 with schizophrenia according to DSM and 44 according to ICD whereas the other was 13 and 24. 

Shows weakness in diagnosis of schizophrenia. 

  1. Validity 

Extent to which we are measuring what are intended to measure. There are a number of validity issues to consider. 

One way to assess validity of diagnosis is criterion validity - do different assessment systems reach the same diagnosis for the same patient. Above research suggest one over-diagnosed or the other under-diagnosed.  Either way, this is poor validity.

  1. Co-morbidity 

The phenomenon where two or more conditions occur together. Schizophrenia is commonly diagnosed with other conditions such as depression and post traumatic stress disorder. This posses a challenge for both classification and diagnosis of schizophrenia.

  1. Symptom overlap 

There is considerable symptom overlap between schizophrenia and other conditions like bipolar disorder which both include symptoms such as delusions and avolition. 

This again questions the


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