Classification and diagnosis of schizophrenia

Classification and diagnosis of schizophrenia

1. Reliability

   • Inter-rater reliability
     • AO1
       • the consistency of the measuring instrument
       • CARSON
         • the DSM-III had fixed the problem of inter-rater validity once and for all
     • AO2
       • WHALEY
         • inter-rater reliability correlations in the diagnosis of Sz, as low as 0.11
         • REJECT-there is a lack of inter-rater reliability, contradicting CARSON
       • COPELAND
         • 69% of US psychiatrists diagnosed Sz with only 2% of British psychiatrists diagnosed Sz
         • differences in DSM and ICD affect diagnosis.
           • AO3-DSM is culturally biased
   • the degree to which different raters give consistent estimates of the same behaviour
   • Test-retest reliability
     • AO1
       • assesses the external consistency of the test
       • WILKS ET AL
         • the test-retest reliability was high when looking at screening tests for Sz
     • AO2
       • ROSENHAN
         • there is difficulty in distinguishing between normality and and abnormality, once admitted patients became their illness
       • PRESCOTT ET AL
         • analysed test-retest of several measures of attention and information in 14 chronic Sz patients found that performances on these measures were stable over 6 months
         • this shows high reliability
         • AO3-longitudinal

2. Validity

   • does the diagnosis represent something real and distinct and measure what it claims to
   • comorbidity
     • AO1
       • presence of one or more additional disorders co-occuring with a primary disorder
       • BUCKLEY
         • comorbid depression occurs in 50% of patients, 47% also have a lifelong diagnosis of comorbid substance abuse, creating difficulties in the diagnosis/treatment
     • AO2
       • WEBER ET AL
         • morbidity and mortality from general medical conditions are elevated among patients with Sz compared with general US population. >50% of those with Sz have one or more comorbid psychiatric or general medical conditions
         • Supports-more than half Sz go on to have another disorder
       • KESSLER ET AL
         • only a minority of those with mental disorders were found to have received professional treatment during the proceeding 12 months. Those with comorbid disorders - more likely to receive treatment however comorbidiity can affect treatment
         • shows that difficulties can occur
   • Predictive validity
     • AO1
       • the degree to which a test accurately predicts a critereon that will occur in the future
     • AO2
       • BENTALL ET AL
         • Sz is not a useful scientific category as symptoms are also found in other mental disorders
         • People with Sz don't always share the same prognosis therefore there is little predictive validity
       • HARRISON
         • social skills, academic achievement and family tolerance may influence prognosis
         • All cases can be different and therefore lacks predictive validity and test-retest reliability is difficult to achieve