validity of diagnosis refers to the accuracy of the diagnosis
the diagnosis should accurately reflect the symptoms that are being experienced by the patient
the diagnosis should have predictive validity
diagnosis of schiz lacks predictive validity as the outcomes vary between patients (rule of thirds)
patients can receive different diagnosis depending on the assessment system used as there are different diagnostic criteria in the ICD and DSM.
cheniaux (2009) found that schiz is more likely to be diagnosed using the ICD than the DSM
the differences in diagnostic criteria (between ICD and DSM) suggest that schiz is over-diagnosed using the DSM or under-diagnosed using the ICD.
this indicates poor validity as patients aren't receiving accurate diagnosis and treatment.
the diagnosis of schiz is also criticised for lacking predictive validity
the outcomes vary greatly between patients with roughly a third of the patients having one episode, a third having an episodic pattern or remission and schizophrenic episodes and a this who have no remission
the symptoms experienced will vary greatly between patients with a diagnosis of schizophrenia
e.g. som e will display positive symptoms of schiz which is very different from those displaying negative symptoms but both receive the same diagnosis of schiz
differences in the diagnostic criteria given in the ICD and the DSM mean that patient can receive a different diagnosis depending on the assessment system used
CHENIAUX et al found that schizophrenia is much more likely to be diagnosed using the ICD than the DSM
suggesting that either schiz is over-diagnosed with ICD or under-diagnosed with DSM, which indicates poor validity, leading to patients not receiving an accurate diagnosis and treatment