Classification and Diagnosis of Schizophrenia

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Clinical Characteristcs of Schizophrenia

  • Positive and Negative Symptons
  • positive symptons reflect an excess or distortion of normal functions and typically add to ones behaviour.
  • Negative symptons reflect a diminition of normal functions. 
  • Under DSM-IVR the diagnosis of schizophrenia requires at least a one month duration of two or more positive symptons. 
  • A: Positive Symptons
  • delusions
  • experiences of control
  • hallucinations
  • disordered thinking
  • B: Negative Symptons
  • affective flattening
  • alogia
  • avolition

Issues of Reliability and Validity

  • Reliability
  • refers to the consistency of a measuring instrument.
  • Reliability of such questionnaires or scales can be measured in terms of whether two independent assessors give similar diagnoses, or whether test used to deliver these diagnoses are consistent over time.
  • Inter-Rater Reliability
  • Publication of DSM-III was designed to provide more reliable system for classifying psychiatric disorders.
  • DSM-III had fixed the problem of inter rater reliability once and for all. 
  • Reliable classification system
  • Test-Retest Reliability
  • Cognitive Screening test are important in diagnosis as they measure the degree of neuropsychological impairment.
  • Two alternate forms of the test were given to schizophrenic patients over intervals varying from 1-134 days
  • Test-retest reliability was high at 84
  • Validity
  • Refers to the textent that a diagnosis represents something real and distinct from other disorders. 
  • Reliability and validity are linked because a diagnosis canont be valid if it is not reliable
  • Comorbidity
  • important issue for validity or diagnosis of mental illness.
  • Refers to the extent that two conditions co occue
  • Common among patients with schizophrenia. 
  • include substance


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