(2026 Exams) Reliability & Validity of Diagnosis

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Reliability of Diagnosis

Reliability refers the consistency of diagnosis, including inter-rater reliability where the same diagnosis is made by two or more assessors.

Cheniaux et al. (2009)

Cheniaux et al. (2009) investigated the reliability of schizophrenia diagnosis.
100 patients were diagnosed by different psychiatrists using both ICD and DSM criteria.

Results of Cheniaux et al. (2009)

Results showed poor reliability.
One psychiatrist diagnosed 26 patients according to DSM and 44 according to ICD, while another psychiatrist diagnosed 13 (DSM) and 24 (ICD).

Validity of Diagnosis - Comorbidity and Symptom Overlap

Validity is the extent to which the methods used to diagnose mental illness are accurate - for example, that the methods are able distinguish schizophrenia from other, similar disorders.

Validity issues

The diagnosis of schizophrenia suffers from a number of validity issues, including:
- Co-morbidity.
- Symptom overlap.
- Gender bias.
- Cultural bias.

Comorbidity

Comorbidity is the extent to which two or more conditions occur together, calling into question the validity of diagnosis.
Buckley et al. (2009) found that around half of all patients diagnosed with schizophrenia also had a diagnosis of depression. This factor called into question the ability to tell the difference between the two conditions and diagnose accurately.
It could be that very severe depression can present as schizophrenia because it looks a lot like it.

Symptom overlap

Symptom overlap refers to the extent to which the symptoms of one disorder are also present in a different disorder.
- For example, schizophrenia and bipolar disorder both include symptoms such as delusions and avolition (lack of motivation to do tasks with an end goal).

Symptom overlap cont.

Symptom overlap also calls into question the ability to accurately diagnose specific conditions.
Under ICD, a patient might be diagnosed with schizophrenia; while under DSM, they might be classified with bipolar disorder.
This might even mean that the two are actually the same disorder.

Rosenhan (1973) - Study on Pseudopatients

The aim of this study was to test the hypothesis that psychiatrists cannot reliably tell the difference between people who are mentally ill and those who are not.

Research method

The main study is an example of a field experiment. The manipulation (independent variable) was the made-up symptoms of the 8 pseudo (fake) patients, and the dependent variable was the psychiatrists' admission and diagnostic label of the pseudo patient.
The study also involved participant observation, since, once admitted, the pseudo-patients kept written records of how the ward operated, as well as how they personally were treated. They telephoned hospitals for appointments and all reported the same symptom, ‘I hear a voice saying thud, empty or hollow’.

Results

All were admitted and all except one given a diagnosis of schizophrenia. They remained in hospital for 7 to 52 days (average 19 days). Visitors to the pseudo patients observed “no serious behavioural consequences”. Although they were not detected by the staff, many of the other patients suspected their sanity (35 out of the 118 patients voiced their suspicions).
Some patients voiced their suspicions very vigorously for example ‘You’re not crazy. You’re a journalist, or a professor. You’re checking up on the hospital’.

Conclusion

The study demonstrates both the limitations of classification and, importantly, the appalling conditions in many psychiatric hospitals. This has stimulated much further research and has led to many institutions improving their philosophy of care.

Evaluation of Rosenhan

Strengths
- Ecologically valid.
- Objective evidence from pseudo patients.
- Quantitative and qualitative data.
- Practical applications.
Limitations
- Ethics.
- The pseudo patients experiences could differ from real patients as they knew they were not mentally ill.