SCHIZOPHRENIA - Reliability and validity of the diagnosis of schizophrenia

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  • Reliability and validity of the diagnosis of schizophrenia (sch)
    • Diagnosis
      • def: identification of the nature and cause of illness
      • 2 commonly used classification systems: DSM-5 AND ICD-10
        • DSM-5 -diagnostic classification system produced in USA
        • ICD-10 - diagnostic classification system produced by the World Health Organisation
    • Reliability
      • def: consistency of diagnosis
      • affects diagnosis in 2 ways:
        • test-retest reliability - occurs when a clinician makes the same diagnosis on separate occasions from the same info
        • inter-rater reliability - occurs when different clinicians make identical, independent diagnosis of the same patient
      • Research
        • Beck (1962) - 54% concordance rate between practitioners' diagnoses when assessing 152 patients
          • Soderberg (2005) reported concordance rate of 81% using DSM. Classification systems more reliable over time
            • Nilsson (2000) - only reported 60% concordance rate between using ICD - DSM = more reliable
        • Read (2004) - test-retest reliability to have 37% concor.rate. 1970 study - 194 British and 134 US practitioners provided diagnosis on case description. 69% US diagnosed sch, 2% British did. Diag of sch = never fully reliable
        • Seto (2004) - sch was labelled 'integration disorder' in Japan due to difficulty in reliable diagnosis. Suggests sch, as a separate & identifiable disorder, doesn't exist
        • Jakobsen (2005) - 100 Danish patients with history of psychosis were assessed using ICD. 98% con.rate = high reliability of clinical diag using recent classifications
      • Evaluation (A03)
        • DSM regarded as more reliable than ICD - symptom outline is more specific
        • Reliablity of sch diag (81%) is higher than that of anxiety disorders (63%)
        • even if reliability is not perfect, they provide practitioners with common language which may lead to better understanding of disorder and development of effective treatment
        • evidence suggests that reliability of diag has improved as class-systems have been updated
    • Validity
      • def: accuracy of diagnosis
      • for valid diag, sch should be a separate disorder, as categorised by symptoms through use of class.systems
      • validity can be assessed in 4 ways:
        • reliability - valid diag must be reliable
        • predictive validity - if diag leads to successful treatment - diag = valid
        • descriptive validity - patients with sch should differ in symptoms from other disorders
        • aetiological validity - all sch should have the same cause for the disorder
      • Research
        • CLASSIC: Rosenhan (1973) - 8 PPs who didn't suffer sch presented themselves to mental hospital, claiming to hear voices. Later, hospital was informed of pseudo-patients would try to get entry over 3 months. Suspected no. recorded.
          • 8 volunteers took between 7-52 days to get out. Normal behavs seen as a sign of sch. 35 / 118 real patients suspected the PPs were sane. During 3 month period, 193 patients were admitted, 83 aroused suspicion of being false patients. No pseudo-patients.
            • Not usual for people to fake insanity - doctors let 8 PPs in to help them, not turn them away
            • expectation effect - doctors expected them to be ill and looked for evidence for it
            • diagnosed as sch is a 'sticky label' - diff to remove with bad consequences
        • Mason (1997) - tested ability of 4 class.sys of diag to predict the outcome of disorder (over 13 years) in 99 sch patients. Modern class.sys = more pred.validity
        • Birchwood & Jackson (2001) - 20% of sch recover and never have another episode, 10% are so affected they commit suicide. Too much variety in outcome of sch for pred.val to be supported
        • Jager (2003) - possible to use ICD to distinguish 951 cases of sc from 51 persistent delusional disorders, 116 acute and transient psychotic disorders and 354 schizoaffective disorders. Suggests diag = high des.val
      • Evaluation (A03)
        • predictive validity of sch diag = low bc diff sufferers experience wide range of symptoms
        • incidence of sch = 1%, while for OCD is 3%. Incidence for co-morbid sch with OCD is much higher - implies existence os separate schizo-obsessive disorder and val of sch diag is low, as sch is not a disorder separate from other disorders
        • Bentall (2003) - diag of sch says nothing about its cause. Diag also says nothing about prevalence rates - differ from urban and rural environments - implies diag is invalid
        • Labelled as sch has long lasting, negative effects (relationships, work, self-esteem etc.) - unfair when diag is made with little validity
        • Kendall & Jablensky (2007) - diagnostic categories are justifiable - give clinicians agreed framework to investigate and discuss people's clinical experiences. Greater understanding = more effective treatment

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