Reliability and Validity

• Reliability

  Diagnosis of schizophrenia must be repeatable, ie 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)
• Validity

  Extent that a diagnosis represent something real and distinct from other disorders and the extent that a classification system measures what it claims to
• Symptom overlap - AO1

  Symptoms of a disorder may not be unique to that disorder but may also be found in other disorders, making diagnosis difficult

  • For example, difficulty concentrating and anhedonia are symptoms of schizophrenia, depression and bipolar disorder

  This creates problems with validity as it makes schizophrenia harder to measure and diagnose - perhaps leading to some patients being treated for the wrong disease
• Co-morbidity - AO1

  two or more conditions or diseases occur simultaneously in a patient (eg schizophrenia and depression)

  Psychiatric co-morbidity is common with schizophrenic patients - including substance abuse, anxiety and depression

  • Buckley et al (2009) - estimated that co-morbid depression occurs in 50% of patients, and 47% of patients also have lifetime diagnosis of co-morbid substance abuse
  • Swets et al (2014) - found that at least 12% of patients with schizophrenia also fulfilled the diagnostic criteria for OCD and about 25% displayed significant obsessive-compulsive symptoms
• Gender Bias - AO1

  The tendency to describe the behaviour of men and women in psychological theory and research that might not represent the characteristics of either gender accurately

  The prevalence of schizophrenia is equal in both genders, however, men are more likely to be diagnosed than women

  • Broverman et al (1970) - clinicians in the US equated mentally healthy adult behaviour with mentally healthy male behaviour, therefore women tended to get diagnosed less
• Cultural differences/bias - AO1

  Culture – the rules, customs, morals, child rearing practices, etc. that bind a group of people together and define how they are likely to behave
• Cultural differences/bias - AO1

  Research suggests there is a significant variation between countries when it comes to diagnosing schizophrenia - therefore, culture has an influence on the diagnosis process

  African-American and Afro-Caribbean English people are 8 times more likely to be diagnosed with schizophrenia

  • This may be due to the idea that in some cultures, hearing voices from ancestors is seen as a gift
  • As its seen positively, people may not feel as if they need help so its harder to diagnose
  • Can also lead to harmful stereotypes of cultures
• Cultural differences/bias - AO1

  Luhrmann et al (2015) - 20 ppts each from India, Ghana and the US. Those from Ghana and India described the voices as positive and motivating, whereas those from the US described them as harmful and violent
• Diagnostic manuals - AO1

  DSM-5 - Can be problematic as it may be difficult to properly and reliably define what is seen as bizarre and what is not

  ICD-10 considers a range of schizophrenic subtypes whereas DSM-5 does not - unreliable between types used

  A kappa score is a statistic which measures inter rater reliability

  • 1 = perfect inter-rather agreement
  • 0 = no agreement
  • 0.7 = generally good agreement
• Symptom Overlap - AO3

  Ellason and Ross (1995) - pointed out that people with DID actually have more schizophrenic tendencies than people actually diagnosed with schizophrenia

  Most people who are diagnosed with schizophrenia have sufficient symptoms of other disorders that they could also receive at least one other diagnosis
• Symptom Overlap - AO3

  Serper (1999) - assessed patients with co-morbid schizophrenia and cocaine abuse, cocaine intoxication on its own, and schizophrenia on its own

  They found that despite there being considerable symptom overlap in patients with schizophrenia and cocaine abuse, it was actually possible to make accurate diagnosis

  Could suggest that symptom overlap could be worked through with more in-depth investigation and diagnosis processes
• Co-morbidity - AO3

  Weber et al (2009) - looked at nearly 6 million hospital discharge records to calculate co-morbidity rates

  Psychiatric and behaviour related diagnoses accounted for 45% of co-morbidity

  However, Many patients with a primary diagnosis of schizophrenia were also diagnosed with medical (non-psychiatric) problems, including hypothyroidism, asthma, and hypertension

  Weber concluded that the nature of a diagnosis of a psychiatric disorder is that patients tend to recover a lower standard of medical care, which adversely affects the prognosis for patients with schizophrenia
• Gender Bias - AO3

  290 male and female psychiatrists read two case articles of patients’ behaviour and then asked them to offer their judgement on these individuals using standard diagnostic criteria

  • When the patients were described as male, or no information was given their diagnostic rate of schizophrenia was 56%
  • When the patients were described as female, only 20% were diagnosed with schizophrenia
• Cultural differences/bias - AO3

  Copeland (1971) - gave 134 US and 194 British psychiatrists a description of a patient

  • 69% of US psychiatrists diagnosed schizophrenia but only 2% of the British ones gave the same diagnosis
  • This suggests that culture bias is an issue as diagnostic criteria can be different when viewed from different cultures, as the contexts from which its arisen can be vastly different
• Diagnostic manuals - AO3

  50 senior psychiatrists in the US were asked to differentiate between ‘bizarre’ and ‘non-bizarre’ delusions, producing an inter-rater reliability score of 0.40