SCHIZOPRENIA - reliability and validity in diagnosing 

RELIBAILITY AND VALIDITY IN DIAGNOSIS 

RELIABILITY

• Diagnosis of schizophrenia must be repeatable and reach the same conclusions at two points in time 

• Inter-rater reliability measured using a kappa score between 0 and 1, 0.7 is considered good

• In DSM-V field trials, diagnosis only had a kappa score of 0.46

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CULTURAL DIFFERENCES IN DIAGNOSIS

• Copeland gave 134 US and 194 British psychiatrists a description of a patient where 69% of US diagnosed but only 2% of British did showing cultural differences can affect reliability of diagnosis 

• Luhrmann found hearing voices influenced by cultural environment as 60 people from Ghana, India and the US were interviewed and those in Ghana and India reported positive experiences of voices such as offering advice whereas US reported more violent and hateful because its more common in the West so isn’t an inevitable feature 

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EVALUATION: RELIABILITY

LACK OF INTER-RATER RELIABILITY ✅

• Little evidence that DSM is routinely used with high reliability by mental health clinicians 

• Whaley - inter-reader reliability correlations in the diagnosis of schizophrenia as 0.11

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UNRELIABLE SYMPTOMS ✅

• For diagnosis, only one of the characteristics of bizarre delusions is required

• When 50 psychiatrists were asked to differentiate between bizarre and non-bizarre delusions, inter-rater reliability correlations were only 0.40

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CULTURAL DIFFERENCES ✅

• Ethnic minorities experience less distress because of protective characteristics and social structures 

• Supported by 184 white Americans, African Americans and Latinos diagnosed with schizophrenia 

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GENDER BIAS 

• Occurs when accuracy of diagnosis is dependant of the gender of an individual 

• Accuracy of diagnostic judgement varies on gender-based diagnostic criteria or stereotypes 

• Some diagnostic criteria in DSM-V argue that criteria are causes towards one gender

• Clinicians in the US equate healthy mental behaviour with male behaviour 

• Women to be perceived as less mentally healthy 

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SYMPTOM OVERLAP

• Despite the claim that classification of positive and negative symptoms would make more valid diagnosis, many are found in other disorders eg bipolar 

• Ellason and Ross = people with DID have more schizophrenic symptoms than those diagnosed 

• Most who are diagnosed have sufficient symptoms of other disorders that they could also receive at least one other diagnosis 

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COMORBIDITY

• Common among patients eg substance abuse, anxiety, depression 

• Buckley = comorbid depression in 50% of patients and 47% have a lifetime diagnosis of comorbid substance abuse 

• Schizophrenia and OCD occur together more than chance would suggest 

• Swets = 12% fulfil the diagnostic criteria for OCD with 25% showing symptoms 

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EVALUATION: VALIDITY

GENDER BIAS SUPPORT ✅

• Loring and Powell = 290 male and female psychiatrists diagnosed two case studies 

• Male or no info = 56%

• Females = 20%

• Gender bias among female psychiatrists as well as male in 1988

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CONSEQUENCES OF COMORBIDITY ✅ 

• Weber = 6 million hospital discharges 

• Primary diagnosis with schizophrenia also diagnosed with medical problems such as asthma, hypertension and diabetes

• Patients tend to receive lower standard of medical care due to psychiatric diagnosis

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DIFFERENCES IN PROGNOSIS ✅

• 20% recover previous level of functioning 

• 10% achieve significant with lasting improvement 

• 30% some improvement 

• There’s little predictive validity 

• Psychosocial factors seem to play a role in outcome 

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