Reliability & validity of classification and diagnosis

• Diagnosis

  Reliability – level of agreement on the diagnosis by different psychiatrists across time and cultures; stability of diagnosis over time given no change in symptoms. I.e. how far can the same diagnosis be repeated?

  Validity – the extent to which schizophrenia is a unique syndrome with characteristic, signs and symptoms
• Diagnosis

  Reliability = the consistency of measurement.

  Think: How should clinicians check that their diagnosis is reliable?

  Diagnostic reliability

  = clinicians must be able to reach the same conclusions at two different points in time (test-retest reliability), or different clinicians must reach the same conclusions (inter-rater reliability).
• Diagnosis

  Reliability= the consistency of measurement.

  Cultural differences in diagnosis. Research show that there is a significant variation between countries when it come to diagnosing schizophrenia.

  • Copeland (1971) gave a description of a patient. 69% of US and only 2%  of British psychiatrists diagnosed schizophrenia.
  • Luhrmann (2015) interviewed 60 adults diagnosed with SZ in Ghana, India and the US. Many of the African and India subjects reported positive experiences with the voices they heard whereas US patients were more likely to report these voices as being violent and hateful.
• AO3 - Diagnosis and classification

  (-) Reliability

  It was originally hoped that the use of diagnostic tools (DSM and ICD) could provide a standardised method of recognising mental disorders. However, the behaviour of an individual is always open to some interpretation. The process is actually more subjective than we hoped. The most famous study testing the subjectivity, reliability and validity of diagnostic tools was Rosenhan et al (1972).
• AO3 - Diagnosis and classification

  (-) unreliable symptoms

  For a diagnosis of Sz, only one of the characteristic symptoms is required - if delusions are bizarre. However, this creates problems for reliability of diagnosis.

  When 50 psychiatrists were asked to differentiate between bizarre and non-bizarre delusion, they produce inter-rater reliability correlations of only around 0.4. This suggests that if this central diagnostic requirement lack sufficient reliability, it cannot be an accurate method of distinguishing between Sz and non-Sz patients
• Diagnosis - Validity

  Gender bias in the diagnosis of schizophrenia is said to occur when accuracy of diagnosis is dependent on the gender of an individual. The accuracy of diagnostic judgements can vary for a number of reasons, including gender biased diagnostic criteria or clinicians basing their judgements on stereotypical beliefs held about gender. 

  • Some diagnostic categories may be biased towards pathologizing one gender rather than the other.
• Diagnosis - Validity

  Symptom Overlap

  Despite the claim that the classification of positive and negative symptoms would make for more valid diagnoses of schizophrenia, many of these symptoms are also found in other disorders, such as depression and bipolar disorder.
• Diagnosis - Validity

  Comorbidity

  Important issue for the validity of the diagnosis of mental illness. It refers to the extent that 2 or more conditions can occur at the same time. Psychiatric co-morbidities are common among patients with schizophrenia. These include substance abuse, anxiety and symptoms of depression

  Other disorders can occur at the same time as schizophrenia making it difficult to diagnose and treat. Buckley reported:

  -50% also have depression 

  -15% also have panic disorder 

  -29% also have post-traumatic stress disorder 

  -23% also have OCD
• AO3 - Validity

  (-) the consequences of comorbidity

  Many studies of co-morbidities with SZ have involved small sample sizes.

  However, Weber et al looked at nearly 6 million hospital discharge records, finding evidence of many co-morbid non-psychiatric diagnoses, including asthma and hypertension.

  The authors concluded that patients with SZ tend to receive a lower standard of medical care, which in turn adversely affects their prognosis.
• AO3 - Validity

  (+) Research support

  Loring and Powell found evidence of gender bias among psychiatrists in the diagnosis of Sz.

  Male and female psychiatrists read 2 cases of patient’s behaviour. If patients described as males or no info was given about gender, 56% of the psychiatrists gave a diagnosis of Sz.

  However, when the patients were described as “female” only 20% were given the diagnosis

  This gender bias was not evident among female psychiatrists, suggesting diagnosis is also influenced by the gender of the clinician