What is schizophrenia and how is it diagnosed?

Schizophrenia occurs in about one percent of the general population  Following a diagnosis of schizophrenia, and with effective treatment, up to 80% of people report good or intermediate outcomes.

Three main symptom clusters have been identified:

Positive symptoms

Positive symptoms are a well-documented feature of schizophrenia and are arguably the most recognisable and conspicuous, and can cause extreme distress to the individual. They include hallucinations, which are defined as a perceptual experience that occurs in the absence of any external sensory input, and are most commonly auditory, although they can occur in any modality. Delusions are also positive symptoms, and involve distortions or exaggerations of inferential thinking, which lack any logical consistency, are not explained by cultural beliefs, and persist regardless of contradictory evidence. Persecutory delusions involve the belief that people are “out to get” the individual, resulting in a lack of trust in others. Delusions of reference refers to the belief that neutral events are directed specifically towards the individual. Somatic delusions involve the belief that the individual has a physical ailment contrary to medical advice. Delusions of grandeur are characterised by an exaggerated belief that the individual has power, ability, or fame.

Negative symptoms

Negative symptoms refer to an absence of normal functions. These include a scarcity of facial expressions of emotion, reduced frequency and range of gestures and voice modulation, restricted eye contact, poverty of speech, reduced social interaction, reduced motivation, poor hygiene, and reduced experience of pleasure manifesting as scarcity of recreation, inability to experience closeness, and reduced interest in sexual activity. Negative symptoms have a significant effect on the day to day functioning of the patient, affecting their ability to manage the disorder and reducing their quality of life.

Disorganisation symptoms

Key features of the symptoms of disorganisation include disorganised speech and behaviour and inappropriate affect. Severely disorganised speech is difficult to follow and may be deprived of content. Disorganised behaviour includes bizarre or inappropriate behaviour, actions or gestures. Inappropriate affect includes exhibiting incorrect emotional responses for a given context. Symptoms of disorganisation have been identified as risk factors for poor illness outcome, and have a significant negative effect on a person’s day-to-day functioning and quality of life.


As some of these symptoms occur with other psychiatric disorders such as major depression, bipolar disorder and post-traumatic stress disorder, a combination of symptoms must be present for a diagnosis of schizophrenia.

Using the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), at least two of the above symptoms need to have been present for at least six months and for a significant portion of time over a one-month period. At least one symptom of delusions, hallucinations or disorganised speech needs to be present, and there also needs to be significant social or occupational dysfunction.

Using the International Statistical Classification of Diseases and Related Health Problems (ICD-10), either at least one symptom of delusions, hallucinations, or thought symptoms (thought echo, insertion, withdrawal, or broadcasting) needs to be present, or at least two symptoms of hallucinations, negative symptoms, catatonic behaviour, or incoherent/irrelevant speech needs to be present for most of the time for at least one month.

April 2019

Last updated at: 4:06 am, 5th October 2021

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