Reliability and Validity in Schizophrenia Diagnosis

• Schizophrenia is diagnosed using a book called the DSM-5. It states to be diagnosed a patient must have at least 2 of the main symptoms for at least 6 months.
• For a study to be reliable, the results of the study must be consistent every time the study is repeated.
• What outlines a reliable diagnosis?


  • For one patient whose symptoms remain the same, different doctors give the same diagnosis consistently.
  • For different patients with the same symptoms, one doctor gives all patients the same diagnosis consistently.
• When is a diagnosis valid?


  • The criteria used to make the diagnosis allow us to correctly identify people who have a particular illness.
  • The doctor doesn’t incorrectly diagnose people who don’t have a particular illness.
• Inter-rater reliability is when multiple people make the same measurement, to see how similar their measurements are.
• Researchers use inter-rater reliability to assess the reliability of a diagnosis of schizophrenia.


  • In 1962, Beck found that schizophrenia diagnoses were 52% similar whereas in 2005, researchers found that they were 81% similar. Suggesting a diagnosis of schizophrenia is becoming more reliable over time.
• Validity of Schizophrenia Diagnosis: Rosenhan's Study


  Rosenhan conducted an observational study, got 8 volunteers, who pretended to have schizophrenia, admitted into hospital. He tested how long it took doctors to declare that the volunteers were healthy. It took the doctors between 7 and 52 days to realise the diagnoses were wrong, and that the volunteers were healthy. The study showed that the diagnosis of schizophrenia can lack validity.
• What are the 4 ways to reduces reliability and validity?

  1. Cultural bias
  2. Gender bias
  3. Co-morbidity
  4. Overlap of symptoms
• What type of cultural bias it is when someone assumes that other cultures behave the same as their own?


  Ethnocentric bias.
• When doctors diagnose schizophrenia, they rely on the social norms of their own culture to decide whether a patient’s behaviours match symptoms of schizophrenia. This means they are more likely to diagnose schizophrenia in patients who are from a different culture to the doctor’s own. So, cultural bias reduces the validity and reliability of a diagnosis.
• Cultural Bias: Study Support


  Cochrane's study: Cochrane conducted a review comparing the number of people diagnosed with schizophrenia in the Caribbean and in Britain. The overall rate of schizophrenia was similar in the Caribbean and in Britain. But they found Afro-Caribbean people were 7 times more likely to be diagnosed with schizophrenia in Britain than in the Caribbean. It was concluded this was due to cultural bias by British doctors.
• What are the two ways in which a doctor can display gender bias?


  1. Alpha bias: over-exaggerating differences in men and women's behaviour
  2. Beta bias: ignoring the real differences between men and women
• Gender Bias: Study Support

  Loring and Powell (1988): They gave male and female doctors identical descriptions of a patient’s symptoms, in which they had varied the patients gender between the 2 conditions. They found that when a patient was described as female - 20% and male - 56% of the doctors diagnosed them as having schizophrenia. This indicates there may be alpha bias in the diagnosis of schizophrenia.
• What does it mean if illnesses are comorbid?


  Two or more illnesses occur together in the same person.
• If two illnesses are often co-morbid, this suggests that the criteria for diagnosing the two illness might be incorrect - they might not actually be two separate conditions.


  Reducing validity of diagnosis
• If a patient has a co-morbid illness, then doctors are more likely to ignore some of the symptoms, therefore different doctors may give the same patient different diagnoses.


  Reduced reliability of diagnosis
• Buckley investigated how many schizophrenic patients had a co-morbid mental disorder.

  He found that 50% of patients had depression and schizophrenia, 47% of patients had an addiction and schizophrenia, and 23% of patients had OCD and schizophrenia.
• What is the term for cycles of pronounced highs in bipolar depression?


  Mania
• Symptom Overlap in Diagnostic Criteria


  • The symptoms of schizophrenia considerably overlap with the symptoms of other disorders
  • Patients might be diagnosed with the wrong disorder, reducing the validity of the diagnosis.
  • Patients might be diagnosed with the wrong disorder, reducing the validity of the diagnosis.
• Symptom Overlap: Study Support


  Ellason and Ross's study

  • Compared symptoms of schizophrenia patients with those of dissociative identity disorder patients.
  • They found patients with dissociative identity disorder displayed more schizophrenic symptoms than patients with schizophrenia.