AO1 - Reliability + Validity in Diagnosis and Classification

• Diagnosis: "The identification of the nature of an illness or other problem by examination of the symptoms (1), e.g. someone reporting hearing voices" (1)
• Classification: "The action or process of classifying something, the classification of a disease according to symptoms (1), e.g. a symptom of schizophrenia is hallucinations" (1)
• Reliability in diagnosis:

  • Reliability refers to consistency - this refers to whether we can gain consistent results when classifying and diagnosing schizophrenia
  • The extent to which different classification systems agree upon how schizophrenia should be classified and the extent to which two or more health professionals would agree on the same diagnosis, regardless of time period or culture, measured by inter-rater reliability
• Validity in diagnosis:

  • Validity refers to accuracy - the extent to which we are measuring what we intended to measure (schizophrenia)
  • For example, are the classification systems accurately outlining the signs and symptoms of schizophrenia, and are health professionals accurately diagnosing schizophrenia?
• Symptom overlap - This is where two or more conditions share similar symptoms. For example, both schizophrenia and depression involve negative symptoms such as avolition
• Co-morbidity - This is where two illnesses/conditions occur at the same time. Schizophrenia is commonly diagnosed with other conditions such as depression and/or OCD as they share common symptoms, e.g. lowered mood

  • This is a problem as it means that schizophrenia may not exist as a distinct condition which may lead to misdiagnosis
• Gender bias - Since the 1980s, men have been diagnosed with schizophrenia more often than women. This may be because men are more genetically vulnerable to developing schizophrenia than women

  • However, this may be because females with schizophrenia typically function better than men, being more likely to work and have good family relationships
• Culture bias - English people of African origin are much more likely to be diagnosed with schizophrenia in the UK - rates in the West Indies and Africa are not high so this cannot be due to genetic vulnerability

  • Higher diagnosis rates in the UK may be because some behaviours classed as positive symptoms are normal in African cultures - e.g. hearing voices as a part of ancestor communication
• Research was conducted by Cheniaux, who asked two psychiatrists to diagnose the same 100 patients using the DSM and ICD. One psychiatrist diagnosed 26 according to DSM and 44 according to ICD. The other diagnosed 13 according to DSM and 24 according to ICD. This shows poor inter-rater reliability and demonstrates poor reliability as both psychiatrists diagnosed almost double the number of patients using the ICD than the DSM, questioning the validity of the diagnosis.