Revise Diagnostic criteria for schizophrenia for Cambridge 9990 (1.1.1)

Symptoms of schizophrenia are typically categorised as either positive or negative. Positive symptoms represent an excess or distortion of normal psychological functions, adding experiences that are not typically present. Key examples include hallucinations, which are sensory perceptions without external stimuli (e.g., hearing voices), and delusions, which are fixed, false beliefs that are resistant to contrary evidence (e.g., paranoid delusions of being watched). Disorganised speech and grossly disorganised or catatonic behaviour are also considered positive symptoms. In contrast, negative symptoms represent a diminution or loss of normal functions. These include affective flattening (a reduced range and intensity of emotional expression), alogia (poverty of speech), and avolition (a severe lack of motivation to engage in purposeful activities). These symptoms are often more persistent and less responsive to medication.

Clinicians use standardised classification systems to diagnose schizophrenia, primarily the DSM-5 and ICD-11. The DSM-5, from the American Psychiatric Association, requires at least two symptoms from a list including delusions, hallucinations, disorganised speech, grossly disorganised behaviour, and negative symptoms. Crucially, at least one of the symptoms must be delusions, hallucinations, or disorganised speech. These active-phase symptoms must be present for a significant portion of a one-month period, with continuous signs of the disturbance persisting for at least six months. The WHO's ICD-11 has slightly different criteria, requiring symptoms to be present for at least one month. It places emphasis on specific 'first-rank' symptoms (e.g., thought echo or passivity experiences), where only one is needed for diagnosis, or two other more common symptoms.

The diagnosis of schizophrenia faces significant challenges regarding its reliability and validity. Reliability refers to the consistency of diagnosis. Inter-rater reliability can be low because the criteria require subjective interpretation of a patient's experiences, meaning two clinicians might reach different conclusions. Validity, the accuracy of the diagnosis, is also questioned. Are we diagnosing a genuine, distinct disorder? Rosenhan's (1973) classic study, 'On being sane in insane places', powerfully challenged diagnostic validity. He had eight 'pseudopatients' feign a single symptom (hearing a voice) to gain admission to psychiatric hospitals. Once admitted, they acted normally but were still diagnosed with schizophrenia, and their normal behaviours were interpreted as pathological. This suggested that the diagnostic labels were 'sticky' and that clinicians could not reliably distinguish the sane from the insane.

Cultural bias is a major threat to the validity of schizophrenia diagnosis. Behaviours and beliefs considered normal in one culture may be viewed as pathological in another. For instance, in some Afro-Caribbean cultures, it is not uncommon to believe in communication with ancestors, which a clinician from a Western background might misinterpret as an auditory hallucination or delusion, leading to a misdiagnosis of schizophrenia. Research in the UK and USA has consistently shown that people of African descent are more likely to be diagnosed with schizophrenia than white people. This suggests that diagnostic manuals, developed within a Western framework, may not be universally applicable, leading to systematic over-diagnosis in certain ethnic groups and questioning the cultural validity of the criteria.