Validity and Reliability in the diagnosis of SZ

• Reliability refers to the consistency of the diagnosis
• Validity refers to the accuracy of the diagnosis
• What can be used to test the reliability of a diagnosis?

  Reliability can be measured by using either test-retest (making the same diagnosis at different times with the same clinician and information provided), and inter-rater reliability (where different clinicians make the same diagnosis of the same person)
• Diagnosis of SZ can change over time. The diagnostic criteria of ICD (10) and DSM (V) change each time they are updated which can affect the validity and reliability of diagnosis
• Co-morbidity is when a person has 2 or more disorders at the same time
• How is Co-morbidity a problem for the validity of a diagnosis?

  1/2 of people diagnosed with SZ also have depression- therefore, it is hard to tell if it is a distinct condition.
• What is symptom overlap and how does it affect validity?

  Symptom overlap is when two disorders share the same symptoms (for example, bipolar disorder and SZ both share symptoms like delusions and avolition)- the lack of distinction questions the validity of the classification and diagnosis of SZ. Bipolar and SZ could be a variation of the same, single condition
• How did Osorio's (2019) study show good reliability about diagnosis?

  Osorio found a inter-rater reliability of +0.97 and test-retest of +0.92. This shows we can be reasonably sure that diagnosis of SZ is consistently applied
• What did Cochrane find about how cultural bias affects validity?

  Cochrane found that incidence of SZ is 1% in both the YK and West Indies- but there is a much higher incidence of diagnosis of people of afro-Caribbean origin in the UK- suggesting British people of AC origin are discriminated against by a culturally biased diagnostic system