2. Discuss validity and reliability of diagnosis
within abnormal psychology means identifying and classifying abnormal
behavior on the basis of symptoms, the patients’ self-reports, observations,
clinical tests or other factors such as information from relatives.
use psychological assessment and diagnostic manuals to make diagnosis. The
diagnostic manuals help to classify and standardize diagnosis.
involves matching the results of the psychological assessment with
classification systems such as DSM-IV-TR and ICD-10. The purpose of
diagnosis is to find a treatment for the patient and to make a prognosis.
in its fourth revised version, is developed by the American Psychiatric
Association. The manual lists what it terms “mental disorders”. For each of
the 300 disorders there is a list of symptoms that the clinician could look
for in order to diagnose correctly. A new fifth version is on its way. The
diagnostic manual does not identify causes of psychological disorders
(etiology) but merely describes symptoms.
International Classification of Diseases) is published by WHO (World Health
Organization). The manual uses the term “mental disorder”. The diagnostic
manual includes reference to causes of the disorders (etiology).
Reliability of diagnosis
in diagnosis means that clinicians should be able to reach the same correct
diagnosis consistently if they use the same diagnostic procedure (e.g.
standardized clinical interview, observation of the patient’s symptoms,
neuropsychological examination with scanners and diagnostic manuals). This
is called inter-judge reliability.
can be improved if clinicians use standardized clinical interview schedules,
which define and specify sets of symptoms to look for. The individual
psychiatrist must still make a subjective interpretation of the severity of
the patient’s symptoms.
introduction of diagnostic manuals has increased reliability of diagnosis
over the year even though the manuals are not without flaws.
of diagnosis is a necessary prerequisite for validity. Rosenhahn (1973)
performed a classic study that challenged reliability and validity of
psychiatric diagnosis and showed the consequences of being labeled as
“insane”. In this study eight pseudo-patients were diagnosed as suffering
from severe psychological disorders but they were in reality imposters.
Cooper et al. (1972) The US-UK Diagnostic Project
The aim of
the study was to investigate reliability of diagnosis of depression and
researchers asked American and British psychiatrists to diagnose patients by
watching a number of videotaped clinical interviews.
psychiatrists diagnosed the patients in the interview to be clinically
depressed twice as often. The American psychiatrists diagnosed the same
patients to be suffering from schizophrenia twice as often.
indicated that the same cases did not result in similar diagnosis in the two
countries. This points towards problems of reliability as well as cultural
differences in interpretation of symptoms and thus in diagnosis.
Validity of diagnosis refers to receiving the correct
diagnosis. This should result in the correct treatment and a
prognosis (predictive validity). Validity presupposes
reliability of diagnosis.
It is much more difficult to provide a correct diagnosis and
give a prognosis for a psychological disorder than for a
physical disorder because it is not possible to observe
objective signs of the disorder in the same way.
The DSM-IV manual does not include etiology but only
symptoms. Sometimes patients have symptoms that relate
to different psychological disorders so it can be difficult to
make a valid diagnosis.
Study: Mitchel et al. (2009) Meta-analysis of validity of
diagnosis of depression
The study used data from 41 clinical trials (with 50,000
patients) that had used semi-structured interviews to
The general practitioners (GPs) had 80% reliability in
identifying healthy individuals and 50% reliability in
diagnosis of depression. Many GPs had problems making a
correct diagnosis for depression.
Generally GPs were more likely to identify false positive signs
of depression after the first consultation. Michel et al. argued
that GPs should see patients at least twice before making a
diagnosis since accuracy of diagnosis was improved in studies
that used several examinations over an extended period.
Evaluation of the study:
(1) The strengths of meta-analysis
are that it can combine data from many studies and it is
possible to generalize to a larger population; (2) Limitations of
meta-analysis are that it may suffer from the problem of
publication bias; since data from many different studies are
used there may also be problems of interpretation of the data
because it is not certain that each study uses exactly the same
Rosenhan (1973) On being sane in insane places
reliability and validity of diagnosis in a natural setting. Rosenhan wanted to
see if psychiatrists could distinguish between “abnormal” and “normal” behavior.
This was a covert
participant observation with eight participants consisting of five men and three
women (including Rosenhan himself). Their task was to follow the same
instructions and present themselves in 12 psychiatric hospitals in the USA.
participants were admitted to various psychiatric wards and all but one were
diagnosed with schizophrenia. The last one was diagnosed with manic
pseudo-patients behaved normally while they were hospitalized because they
were told that they would only get out if the staff perceived them to be
pseudo-patients took notes when they were hospitalized but this was
interpreted as a symptom of their illness by the staff. It took between 7 to
52 days before the participants were released. They came out with a
diagnosis (schizophrenia in remission) so they were “labeled”.
study was done later where the staff at a specific psychiatric hospital were
told that impostors would present themselves at the hospital and that they
should try to rate each patient whether he or she was an impostor. Of the
193 patients, 41 were clearly identified as impostors by at least one member
of the staff, 23 were suspected to be impostors by one psychiatrist, and 19
were suspected by one psychiatrist and one staff member. There were no
controversial study was conducted nearly 40 years ago but it had an enormous
impact in psychiatry. It sparked off a discussion and revision of diagnostic
procedures as well as discussion of the consequences of diagnosis for
patients. The development of diagnostic manuals has increased reliability
and validity of diagnosis although the diagnostic tools are not without
used raises ethical issues (the staff were not told about the research) but
it was justified since the results provided evidence of problems in
diagnosis which could benefit others. There were serious ethical issues in
the follow-up study since the staff thought that impostors would present,
but they were real patients and may not have had the treatment that they