reliability and validity of diagnosis

• Validity is the extent to which schizophrenia is accurately classified as a unique syndrome with characteristics, signs and symptoms
• There is considerable overlap between the symptoms of SZ and other conditions like bipolar disorder (symptom overlap) This lowers the validity of the classification and diagnosis of SZ and increases the chance of misdiagnosis
• Co-morbidity is the extent to which 2 or more conditions occur together and is common in patients with SZ this lowers the validity of classification and diagnosis of SZ
• 
  

  DSM ICD

  Psychiatrist 1 26 44

  Psychiatrist 2 13 24

  
  

  Inter-rater reliability is poor (differences between each psychiatrist even when using the same diagnostic manual)
• strength

  Serper et al. (1999) assessed patients with co-morbid SZ & cocaine abuse, just cocaine abuse and just SZ. They found that despite considerable symptom overlap in schizophrenia and cocaine abuse, it was possible to make accurate diagnosis
• weakness

  Ketter (2005) points out that misdiagnosis due to symptom overlap can lead to years of delay in receiving relevant treatment, during which time suffering and further degeneration can occur