For any diagnostic system to work effectively, it must possess reliability and validity. Reliability means that there is good consistency over time and between different people’s diagnosis of the same patient; the latter is known as inter-judge (or inter-rater) reliability. If a diagnosis of schizophrenia is valid then patients who are diagnosed as suffering from schizophrenia must have the disorder. If a diagnostic system is to be valid, it must also have high reliability. Clearly if a disorder cannot be agreed upon (so low reliability) then all of the different views cannot be correct (so low validity). Whereas a diagnostic system can be reliable but not valid—it can produce consistently wrong diagnoses.
In terms of classification, DSM-IV and ICD-10 take a categorical approach, which assumes that all mental disorders are distinct from each other, and that patients can be categorised with a disorder based on their having particular symptoms. However, diagnosing abnormality is not as straightforward as this approach suggests.

Issues in the classification and diagnosis of schizophrenia: Comorbidity

This refers to a patient who suffers from two or more mental disorders at the same time. Patients with schizophrenia often have other disorders such as major depressive disorder or bipolar disorder or an anxiety disorder. Comorbidity happens because some symptoms are the same across disorders. This creates problems of reliability as there can be inconsistency in which disorder is diagnosed.

  • Sim et al.’s (2006) study of 142 hospitalised schizophrenic patients, 32% of whom had an additional mental disorder.


Issues in the classification and diagnosis of schizophrenia: The continuity approach

This suggests that there is a continuum between schizophrenia and normality.

  • Chapman et al. (1994, see A2 Level Psychology page 381) have found evidence for schizotypy, which is a proneness to developing psychosis (especially schizophrenia). This supports the continuity hypothesis and reduces the reliability with which schizophrenia is diagnosed.


The five types of schizophrenia

The five types raise issues of reliability and validity:

  • Some of the types of schizophrenia have no symptoms in common, which questions if they can be the same disorder.
  • The undifferentiated schizophrenia type raises issues of reliability and validity because it is basically a “rag bag” category for all those patients with schizophrenia who are hard to classify. There is such diversity of symptoms that two patients with undifferentiated schizophrenia might have no common symptoms.
  • Another issue is residual schizophrenia. There can be inconsistency in judgements as to whether schizophrenia cases have reduced sufficiently to be categorised as residual. It can also be difficult to decide if the patient has recovered or still has residual schizophrenia.

Rosenhan’s (1973) research on “being sane in insane places”
  • Rosenhan (1973, see A2 Level Psychology pages 382–383) found hospital staff could not distinguish between the sane and the insane. This was because they failed to detect pseudo-patients who had faked symptoms (reported hearing indistinct voices saying “empty”, “hollow”, and “thud”) to gain admittance to 12 different psychiatric hospitals and once admitted behaved in a normal manner and said they had no further symptoms to the hospital staff. Seven out of eight participants were diagnosed with schizophrenia. This clearly questions the reliability and validity of diagnosis.


  • Errors made in diagnosis may not be representative of diagnosis under more typical circumstances as psychiatrists do not expect people to fake mental illness. Kety (1974, see A2 Level Psychology pages 382–383) has countered this by pointing out that if a patient faked physical symptoms, then they may similarly be mistakenly diagnosed with a physical illness.
  • The psychiatrists may not have been completely convinced. The pseudo-patients were given a very rare diagnosis of “schizophrenia in remission” and most were released in a few days, which suggests the psychiatrists were unconvinced that the patients had really suffered from schizophrenia.


Content validity

This refers to the extent to which an assessment measure covers the range of symptoms of schizophrenia. Thus, the diagnostic manuals have content validity if they provide detailed information regarding all of the symptoms of schizophrenia.

  • Jakobsen et al. (2005, see A2 Level Psychology pages 383–384) used the Operational Criteria Checklist (OPCRIT), a symptom checklist with a glossary providing clear and explicit descriptions of the symptoms, to study patients with a history of psychosis. There was good agreement on the diagnosis of schizophrenia when the diagnoses of OPCRIT were compared against those of ICD-10, indicating a high level of reliability.


  • There was also good agreement (and thus high reliability) when ICD-10 and DSM-IV diagnoses were compared. Both of these findings support content validity as the findings suggest they have sufficient detail of symptoms for accurate diagnosis.
  • Measures such as standard semi-structured interviews or the Operational Criteria Checklist possess good content validity. This is because they involve working through all of the symptoms associated with schizophrenia and with other related mental disorders.


Criterion validity

Any form of assessment for schizophrenia possesses good criterion validity if those diagnosed as having schizophrenia differ in predictable ways from those not diagnosed as schizophrenic.

  • Comer (2001, see A2 Level Psychology page 384) found that people with schizophrenia are much less likely than non-schizophrenics to be in full-time employment and to have a strong social network.
  • This provides some support for criterion validity but it is not especially convincing. This is because individuals suffering from almost any mental disorder are more likely than healthy individuals to experience social, relationship, and job problems, and so this doesn’t distinguish schizophrenics from patients with other mental disorders.


The onset of schizophrenia is typically in the late teens and the mid-30s. About 1% of the population of cultures suffers from schizophrenia during their lives. The symptoms vary somewhat but typically include problems with attention, thinking, social relationships, motivation, and emotion.

Physical and Psychological Symptoms of Schizophrenia

Physical/ behavioral symptoms:

  • Schizophrenics may experience psychomotor poverty (lack of movement) and in extreme cases catatonia, when awkward postures are assumed and the schizophrenic remains motionless in this position for hours at a time. They can exhibit “waxy flexibility” during which their body can be manipulated into different positions.
  • Schizophrenics may fall into a catatonic stupor, during which they lie motionless and appear unaware of their surroundings but are fully conscious throughout.
  • Or increased motor activity can occur, such as stereotypy, purposeless, and repetitive movement.
  • Disorganised, chaotic, and bizarre behavior can be linked to other symptoms, e.g. covering up all the windows with black paper as a result of cognitive disturbance.

Perceptual symptoms:

  • Hallucinations: auditory hallucinations are most common when the schizophrenic hears voices that are often abusive or offer a critical running commentary on their behavior.
  • Visual, smell, and taste hallucinations may also be experienced but are less common.

Cognitive symptoms:
Thought disorders include delusions and thought interference.

  • Delusions of grandeur, persecution, paranoia, and control (sometimes known as alien control symptoms as the schizophrenic believes that their behavior is under external control) can occur, which can develop during the course of the illness into an increasingly complex web of delusion.
  • Thought insertion (a belief that ideas are being planted in their mind), withdrawal (the belief that thoughts are being removed from their mind), and broadcasting (a belief that others can “tune into” their thoughts) can occur—these are collectively known as thought interference symptoms.
  • Cognitive impairments include intellectual deficits in learning and memory.
  • Most evident are the language impairments such as repeating sounds (echolalia), inventing words (neologisms), jumbled speech (word salad), and nonsensical rhyming (clang associations). The speech is characterized by incoherence and abrupt changes of topic due to cognitive distractibility (inability to maintain a train of thought).

Social symptoms:
Schizophrenics usually show social withdrawal and may have always lacked social skills. They have little interest in social interactions and do not gain pleasure from them, and so may be aloof, reclusive, and emotionally distant even before the onset of the disorder.

Emotional/mood symptoms:

  • Symptoms can include a lack of emotion (emotional blunting) or inappropriate affect (e.g. giggling when told of bereavement).
  • One-third of patients suffer depressive symptoms and one in eight patients meet the criteria for a mood disorder as well as schizophrenia and so tend to be diagnosed with schizo-affective disorder. Apathy and a lack of drive, interest, personal care, and hygiene are common and can be linked to the depressed state.


Classification of Schizophrenia

DSM-IV (Diagnostic and Statistical Manual, 4th edition; see A2 Level Psychology page 378), which is the American classification system, and ICD-10 (International Classification of Diseases), the tenth edition of which was published by the World Health Organization in 1992 (ICD-10; see A2 Level Psychology page 378), are the two most common classification systems.

The DSM-IV diagnostic criteria are:

  1. Two or more of the symptoms identified above for a period of over 1 month. One symptom only is needed if the delusions are bizarre or if the hallucination is critical and abusive of the individual’s behavior.
  2. The disturbance must be evident over a significant period of time, at least 6 months, including 1 month of pronounced symptoms.
  3. The symptoms must have led to a failure to function in social and occupational roles.

The ICD-10 criteria are very similar to those used in DSM-IV. The main difference being DSM-IV requires evidence of continuous disturbance for at least 6 months, whereas ICD-10 requires that symptoms must be present for most of the time over a 1-month period.

Types of schizophrenia

DSM-IV identifies five types of schizophrenia: disorganized, catatonic, paranoid, undifferentiated, and residual.
Another common classification is into the positive symptoms (hallucinations, delusions, thought disturbances) of type I schizophrenia or acute disturbance; and the negative symptoms (lack of interest, emotion, motivation, social withdrawal) or type II schizophrenia or chronic disturbance.