Validity and reliability of diagnosis

Definition of validity in reference to diagnosis

If the diagnosis is VALID, the diagnosis system (ICD-10/ DSM-5) accurately describes schizophrenia, and if diagnosed, the person actually has schizophrenia.

This means the diagnosis is accurate.

Kinds of validity in diagnosis

• Concurrent validity

If a patient is diagnosed with 2 or more different tests, and the same diagnosis is given with each test.

• Predictive validity

If the diagnosis from a test can be used to predict outcomes, e.g. response to treatment.

Research

• Explain the method of 2 researchers and their conclusions

Cheniaux et al (2009):

• 2 psychiatrists independently diagnosed 100 patients.

• Used both DSM and ICD criteria.

• 39/40 were diagnosed with schizophrenia using DSM.

• 68/100 were diagnosed with schizophrenia using ICD.

Conclusions - There’s an issue with the validity of these diagnoses.

- There’s low concurrent validity between ICD +DSM in diagnosing schizophrenia.

Rosenhan (1973):

• Covert/ naturalistic method.

• 7 pseudo patients “hollow”, “thud”.

• Different hospitals in the USA.

• Diagnosed with schizophrenia (and 1 with bipolar).

• Normal behaviour was misinterpreted as ‘abnormal’.

• In a follow-up study, 44% of patients were judged by staff to be pseudo patients, but there weren’t any.

Conclusions - Diagnoses were not valid, as the doctors could not tell the ‘sane’ from the ‘insane’ patients.

Definition of reliability in reference to diagnosis

If the diagnosis is RELIABLE, it means that the same patient is being diagnosed using the same system/ method by 2 or more clinicians, and they have diagnosed that patient with the same disorder.

This means the diagnosis is consistent.

Kinds of reliability in diagnosis

• Test re-test

If a clinician using the same test makes the same diagnosis on the same patient at different points in time.

• Inter-rater reliability

If 2 or more clinicians using the same test on the same patient reach the same diagnosis.

Research:

• Explain the method of two researchers and their conclusions

Cheniaux et al (2009)

• Using the same methods;

- Psychiatrist 1: Diagnosed 2 people with schizophrenia with DSM.

- Psychiatrist 2: Diagnosed 13 people with schizophrenia using ICD.

• This suggests that whether or not you get diagnosed with schizophrenia depends on the doctor you go to. The diagnoses are not consistent.

• The negative label associated with schizophrenia could negatively impact a persons life, e.g. employment, social life, and / they may not be getting the treatment they need.

Jakobson

• Found 98% inter-rater reliability for the ICD when 100 danish patients were diagnosed by different clinicians.