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7 Cards in this Set
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ISSUES OF RELIABILITY Reliability
Refers to the consistency of a measuring instrument, to assess, for example the severity of scz symps. Reliability of such questionnaires or scales can be measured in terms of whether two independent assessors give similar diagnoses (inter-rater reliability) or whether tests used to deliver these diagnoses are consistent over time (test-retest reliability). |
ISSUES OF RELIABILITY Inter Rater Reliability
The publication of DSM3 in 1980 was designed to provide a much more reliable system for classifying psychiatric disorders. In a review of the success of DSM3, Carson 1991 claimed that DSM3 had fixed the problem of IRR once & for all. Psychiatrists now had a reliable classification system, so this should have led to much greater agreement over who did, or did not, have scz. |
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ISSUES OF RELIABILITY Test Retest Reliability
Cognitive screening tests such as RBANS are important in the diagnosis of scz as they measure the degree of neuropsychological impairment. Wilks et al 2003 - Administered two alternate forms of the test to scz patients over intervals varying from 1-134 days. The TRR was high at 0.84. |
EVALUATION - ISSUES OF RELIABILITY Inter-Rater Reliability
Despite the claims for inc R in DSM3, over 30 yrs later there is still little evidence that DSM is routinely used with high reliability by MH clinicians. Whaley 2001 - Found IRR correlations in the diagnosis of scz are illustrated in Rosenhams study. |
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EVALUATION - ISSUES OF RELIABILITY Unreliable symptoms
For a diagnosis of scz, only one of the characteristic symptoms is required 'If delusions are bizarre'. However, this creates a problem for diagnosis. Mojtabi & Nicholson 1995 - When 50 senior psychiatrists in the US were asked to differentiate between 'bizarre' and 'non-bizarre' delusions, they produced inter-reliability correlations of only around + 0.40, forcing the R's to conclude that even this central diagnostic requirement lacks sufficient reliability for it to be a reliable method of distinguishing between scz and non-scz patients. |
EVALUATION - ISSUES OF RELIABILITY Test Retest Reliability
Measures of cognitive functioning are vital in the diagnosis of scz, therefore must have TRR to be useful in this role. Prescott et al 1986 - Analysed the TRR of several measures of attention and info processing in 14 chronic scz. Performance on these measures was stable over a 6 month period.
Comparing DSM and ICD
Cheniaux et al 2009 - Investigateed the IRR of the diagnosis of scz according to both DSM-IV and ICD-10. Although the IRR was above +0.50 for both classificatory systems, scz was more frequently diagnosed according to ICD-10 than DSM-IV criteria. |
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ISSUES OF VALIDITY
Refers to the extent that a diagnosis represents something that is real and distinct from other disorders and the extent that a classification system such as ICD or DSM measures what it claims to measure. Reliability and validity are inextricably linked because a diagnosis cannot be valid if it is not reliable. |
ISSUES OF VALIDITY Comorbidity
It is an important issue for the validity of diagnosis of mental illness. It refers to the extent that two (or more) conditions co-occur. Psychiatric comorbidities are common among patients with scz.
Buckley et al 2009 - Estimate that comorbid depression occurs in 50% of patients and 47% of patients also have a lifetime diagnosis of comorbid substance abuse. Such comorbidity creates difficulties in the diagnosis of a disorder and also in deciding what treatment to advise. |
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ISSUES OF VALIDITY Positive or Negative Symptoms
Klosterkotter et al 1994 - Assessed 489 admissions to a psychiatric unit in Germany to determine whether +/- symptoms were more valid for a diagnosis of scz. They found that + symps were more useful than - symps for diagnosis. |
ISSUES OF VALIDITY Prognosis
People diagnosed as scz rarely share the same symps, or share the same outcomes.
Bentall et al 1988 - The prognosis varies with about 20% recovering their previous level of functioning, 10% achieving lasting improvements and about 30% showing some improvement with intermittent relapses. A diagnosis of scz has little predictive validity - some people never appear to recover, but some do. |
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EVALUATION - ISSUES OF VALIDITY Comorbidity & Medical Complications
The poor levels of functioning found in many scz's may be less a result of their psychiatric disorder and more to do with their untreated comorbid physical disorders.
Weber et al 2009 - Examined nearly 6 million hospital discharge records to calculate comorbidity rates. Psychiatric and behavioural related diagnosises accounted for 45% of comorbidity. The study also found many comorbid non-psychiatric diagnoses. They found that some that are diagnosed with scz receive a lower standard of medical care, in turn affecting prognosis. |
EVALUATION - ISSUES OF VALIDITY Comorbidity & Suicide Risk
People with scz pose a relatively high risk for suicide, with comorbid depression being the major cause of suicide beh.
Kessler et al 1994 - Found that the rate for attempted suicide among patients in the National Comorbidity Survey, rose from 1% for those with scz alone to 40% for those with at least one lifetime comorbid mood disorder. |
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EVALUATION - ISSUES OF VALIDITY Ethnicity may lead to misdiagnosis
R suggests that within the UK and elsewhere the rates of scz among African-Caribbean are much higher when compared to white populations.
Harrison et al 1997 - Reported that the incidence rate for scz was 8x higher for A-C groups (46.7 per 100,000) than for white groups (5.7 per 100,000). Some of the increase can be explained by poor housing, unemployment and social isolation. There also remains the misdiagnosis part, factors such as cultural differences in language & mannerisms and difficulties relating with black patients and white clinicians. |
EVALUATION - ISSUES OF VALIDITY Symptoms
Despite the belief that identification of the symps of scz would make for more valid diagnoses of the disorder, many of these symps are also found in other disorders.
Ellason and Ross 1995 - Point out that people with Dissociative Identity Disorder actually have more scz symps than people diagnosed as being scz. |
