Discuss issues of reliability and validity associated with the classification and diagnosis of Schizophrenia. - 24 mark essay

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Discuss issues of reliability and validity associated with the classification and diagnosis of
Schizophrenia (8+16)
Schizophrenia (sz) is a psychological illness characterised by the inability to tell the difference between reality and
fantasy. Patients experience both positive and negative symptoms and in order to be diagnosed sz, a patient must
have had the disorder present for longer than one month and affect their day to day living. Psychologists use either
DSM-IV-TR or ICD-10 to diagnose sz. This essay will explore issues of reliability and validity.
Reliability refers to the consistency of a measuring instrument; the two methods used are test-retest and inter - rater
reliability. Test ­ retest refers to whether the results of the study are the same if repeated, if so, and then it is
reliable. Wilkes et al (2003) administered 2 alternate forms of the test to sz patients over intervals varying from
1-134 days, suggesting reliability. However, this test is unreliable, as the test-retest means that the results must
change the second time if participants have previously done the same test before. This suggests that there are
methodological issues surrounding determining reliability. Read (2004) suggested that test-retest only had a 37%
concordance rate, suggesting that the reliability associated with the classification and diagnosis of sz is unreliable. In
addition, Wilkes (2003) is supported by Prescott (1986) who found that sz scored the same on cognitive impairment
tests over a 6 month period. A particular strength of this study was it was longitudinal, conducted over a long period
over time, which increases its reliability.
Another method of measuring the reliability of a measuring instrument is inter - rater. This refers to the extent by
which two psychologists give the same diagnosis of sz. Carson (1991) claimed that the DSM ­III had fixed the problem
of inter-rater reliability once and for all. This study is flawed, as it is out-dated in regards to the DSM, as later
publications have proven it is still a problem. Willson (2000) found a 60% concordance rate between psychologists
using the ICD-10, which suggests the DSM-IV is more reliable at 74%. This inter-rater reliability is flawed, as all
psychologists reviewing the study were from America, which implies cultural bias. This also show issues in Carson's
(1991) study, as inter-rater still does not have a 100% concordance rate. Also, showing methodological issues with
inter-rater reliability is Beck (1962) who found 54% of psychologists agreed on the diagnosis of 153 patients. This is
a small sample size and just over half of psychologists can agree on a diagnosis, suggesting that there is an issue with
reliability. However, this supports Carson's study later by showing that reliability is improving. Cultural differences in
diagnosis of sz show that there is variation between countries. Coupeland (1971) gave 124 US and British
psychiatrists a description of a patient. Only 69% of the US psychiatrists diagnosed sz and only 2% of British
psychiatrists' diagnosed sz. This shows a real methodological issue with inter-rater reliability in the way that it is
diagnosed. This study is culturally bias and temporally bias, which may also show that opinions are out-dated and have
changed. This study is also further supported by Rosenham (1973) who carried out 2 studies in US psychiatric
hospitals. The first study showed 7/8 ordinary people who were diagnosed with sz into a psychiatric hospital and the
second study showed that 10% of patients were suspected of being fake, showing the difficulty in distinguishing
between normality and abnormality. This study only test-retested once, which means that it lacks reliability. It is also
culturally bias, so people are over-diagnosed even if they are not sz. Cultural differences show that reliability is not
consistent, making classification inconsistent.
Test ­ retest has been found to be difficult in determining the reliability of the classification and diagnosis of sz, as
the test is repeated, making the test an unfair representative of results. The studies are based on observation, which
means that the results may be subject to experimenter bias and may be susceptible to unreliable results. Test ­retest
does not look at the biological approach, which reduces sz to a less complex illness than it is; it does not look into
other explanations for the causes of sz or the fact that there are individual differences, so people will behave
differently and may have a different form of sz. The participants have no free will in the studies, as they have no
control over their illness; however it is arguable that they have free will, as they chose to be a part of the studies and
the test ­ retest is flawed because the participants remember the answers to taking the test before. The studies
regarding test ­ retest are all ethnocentric, suggesting that the results cannot be applied to all cultures and that
some people may be misdiagnosed for sz in other cultures. Inter ­ rater reliability refers to the extent to which two
psychiatrists can make the same diagnosis, however the reliability is questionable when psychiatrists cannot make
the same diagnosis. This may be because classification is determined by culture, which suggests that results are
ethnocentric, and that the diagnosis is not consistent in all cultures. As psychiatrists cannot agree, it reduces the
illness to something less complex than it is, as in the US people are over diagnosed, meaning that it may not be sz
which they are diagnosing. The ethics of testing this are also questionable, as Rosenham's study shows the effects of
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This nurture approach does not look into genetics,
only how the person behaves, which is misleading as there are individual differences, which leads to unreliable
methods of diagnosing people. Test ­ retest and inter ­ rater reliability have issues with diagnosing and classifying
people as sz, as test ­retest fails to recognise the fact that people will remember the study they did before, which
means the results are unreliable.…read more

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