Validity

Diagnostic and criterion validity

• diagnostic validity - refers to the extent that sz represents something that is real and distinct from other disorders an the extent that a classification system such as ICD or DSM measure, what it cleans to measure

Criterion validity - is the extent to which using different classification systems produces the same diagnosis in the same patient. If there are differences here then it suggests there is a lack of agreement over what schizophrenia actually is. Elie cheniaux et al had two psychiatrists independently rate 100 clients using the DSM4 and ICD10, 68 were diagnosed using ICD criteria and 39 with DSM. this suggest criterion validity is low

What factors affect validity?

• Comorbidity

• Symptom overlap

Comorbidity

Refers to the extent that 2 (or more) conditions co occur in the same individual

Psychiatric comorbidities are common amongst patients with schizophrenia. This makes descriptive validity very difficult to achieve as it suggests that SZ may not actually be a separate disorder, as if conditions occur together frequently they might be a single condition

• Buckley et al review found that Comorid depression occurs in 50% of sz patients, 23% OCD, 29% PTSD, 47% substance abuse (making validity very difficult to achieve)

Symptom overlap

Symptoms of sz are also found in other conditions

One of the biggest problems is in differentiating sz from bi polar disorder which can also involve delusions and negative symptoms like avolition

This maes SZ hard to distinguish and can lead to inaccurate diagnosis

• Schneider argued ‘first rank’ symptoms should make its description validity higher. However schizophrenia is not

Pathognomonic - does not have unique symptoms making it hard to differentiate from other disorders

Culture bias

Schizophrenia is statistically more frequent in the UK and elsewhere in people from African Caribbean descent than other groups. Given that rates in African and the West Indies are not that high, this is not die to genetic vulnerability.

Pinto and jones estimates it was 9 times higher in British people of African Caribbean origin than white British groups. This could be to do with psychosocial factors and stressors - poor housing unemployment and social isolation but the most likely explanation is that it is due to the fact that most births psychiatrists are white and biased when judging people from other ethnic backgrounds

Gender bias

Men have been more commonly diagnosed with SZ than women and it tends to be diagnosed earlier in men

Loring and Powell randomly selected 290 make and female psychiatrists to read two case articles of patients behaviour and then asked them to offer their judgment on these individuals using standard diagnosticians criteria. When the patient described as ‘male’ or no info was given about their gender, 56% were given a diagnosis of SZ. However when the patient was decided as female only 20% were given a diagnosis of SZ

This gender bias did not appear to be evident amongst female psychiatrists. This suggests that diagnosis is influenced not only by the gender if the patient but also the gender of the clinician