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Diagnosis in Psychiatry
Alan B. Doris


The first day of my psychiatric career and I am being driven to an out-patient clinic held in a grey concrete block of a GP surgery on the western edge of Edinburgh by my boss, mentor, and trainer Dr P.  “So doctor, what do you think the most common diagnosis I make in this clinic is?” he asks. Oh dear, I know these psychiatrists sometimes like to play mind games, could this be a trick question to show me up as a bumbling beginner before I have even got started. Outside the car are blocks of high-rise flats with a row of drab one storey buildings at their feet – a grocer with wire mesh protecting the windows, a pub scrawled with graffiti and a bookmaker with a few young men shuffling around outside smoking. With some trepidation, “Depression” I answer knowing that this is a common disorder and surely must be rife in this place. Dr P does not even glance towards me as he quickly says “No, try again” – I now know he has played this game before and was ready for my first attempt. “Generalised Anxiety”, I answer – I have read that anxiety disorders are even more common than depression in the community. “Wrong again”. I feel certain now I am being walked towards some punchline by Dr P where my naivety is confirmed and my position in the medical hierarchy made clear to me. I pause, consider again, and with some sense of futility, but with a good knowledge of my fellow Scots vulnerabilities, I make my third attempt with “Alcohol Dependence”. Dr P does not even bother to dismiss my answer this time. I can see in his profile a self-satisfied grin; undoubtedly, I am just the latest in a long line of junior psychiatrists he has played his game with. “The most common diagnosis I make in this clinic is “No Mental Illness””.

This was in 1993 at a time when the unemployment rate in Scotland was over 10%, there was considerable economic deprivation and major problems with drug and alcohol abuse with the consequent scourges of crime and HIV/AIDS. These problems were particularly bad in the housing estates on the fringes of the main cities. At that first clinic, and through the rest of my six months with Dr P he taught the science and art of diagnosis in psychiatry. I am sure “no mental illness” was not his most common diagnosis, though the point he was wanting to make with me from the outset was the importance of considering the wider context of the patient’s life to best understand their distress and so to find ways to help them.  Undoubtedly, there were high rates of mental disorder in the people referred to see Dr P, though not all distress or dysfunction in a person’s life must be given a medical diagnosis. As a “social psychiatrist” Dr P was eager to ensure that societal causes of mental distress such as poverty and unemployment were not ignored by applying a diagnosis and treatment to an individual. Trying to solve an individual’s mental distress with medication or psychotherapy rather than addressing the societal issues would not address the underlying cause.

Dr P was a man of his time, and it is much more likely now that a psychiatrist in the UK, Australasia or North America assessing someone referred to them will make a psychiatric diagnosis, or perhaps more than one. It is crucial that this is done thoughtfully as a psychiatric diagnosis can greatly affect an individual’s life. It can make a person feel validated and understood; lead to effective treatment and support which improves quality of life; entitle the person to financial benefits, or even excuse the person for behaviour which would otherwise by punished through the legal system. On the other hand, being diagnosed with a psychiatric disorder can lead to social stigma and discrimination, affect employment options, or lead to restriction of liberties. In psychiatry as in other areas of medicine “over-diagnosis” can lead to considerable problems for the individual, and there is increasing interest in how to counteract this[i][ii]  An incorrect diagnosis can take a long time to be corrected with possible harm and missed opportunities resulting.  It is therefore important that great care is taken to ensure any diagnosis made is valid and has been made in as reliable a way as possible.


Why Make a Diagnosis?


In all areas of clinical medicine, correct classification, or diagnosis, of the pathological process and its effect on the person is essential. It allows clinicians to use the large body of knowledge about other people who have had the same health problem to better understand the cause, choose treatment, and predict the likely future course for the patient now requiring care. In psychiatry, diagnosis is just as essential, though additional factors are often more important than in other areas of medicine, such as the person’s social and family circumstances, personality, lifestyle, and attitude towards their health. To be useful in planning treatment a psychiatric diagnosis must be embedded in a “formulation” to explain why this person has become unwell in this way at this time in their life; to understand their strengths, and what the best options are for intervention.

A diagnosis may be crucial to non-clinical professionals and organisations to assist them in correctly carrying out their functions. For example, government agencies or insurers to decide entitlement to financial benefits or compensation; recruiters to decide on a person’s suitability for employment; the courts to determine responsibility for offending behaviour, or scientists when carrying out research. In these circumstances, the focus is usually on whether a person has a diagnosable disorder, and if so what, rather than making a diagnosis as part of a formulation for the clinical purpose of aiding treatment planning and improvement of the person’s health.


How is a Diagnosis Made?


The process of reaching a medical diagnosis involves obtaining an account from the patient of their symptoms, looking for signs of physiological abnormality with a physical examination, and considering results from investigations such as blood tests, scans, and x-rays. Putting all this information together leads to a diagnosis which is usually based around the biological system or tissue which is malfunctioning, and the cause of the malfunction such as a bug, inflammation, or abnormal tissue growth.

The diagnoses which traditionally fall within the area of psychiatry involve abnormality of the person’s thoughts, perceptions, emotions, speech, and behaviour. For most psychiatric diagnoses there is currently no measurable underlying biological abnormality. Therefore, most diagnoses are based on patterns of abnormality described by the patient or someone who knows them well, or signs of abnormality in what is said, how it is said, and how the person behaves which a clinician can experience directly during a clinical interview. A key aim of the psychiatrist is to understand as completely and accurately as possible what the patient is experiencing. This is done by the psychiatrist asking the patient to describe their life, both in the past and currently, and how their thoughts, feelings and internal mental experiences affects their life and relations with other people. As the psychiatrist gathers information from the patient, a detailed picture is built up in the psychiatrist’s mind of what the patient’s internal mental world is like. Following this “empathic method” allows the psychiatrist as closely as possible to understand any pattern of abnormality in thinking, emotion, relationships, and behaviour the person has and so to accurately make a diagnosis. Being skilled in this process and having thorough theoretical knowledge of normal and abnormal human psychology (psychopathology), is essential for a psychiatrist[iii].

Psychiatric training usually involves being critiqued by a senior trainer over hundreds of different assessments and then continually refining these skills over the thousands of patients most psychiatrists will assess during their subsequent career. Experienced clinicians often reach a diagnosis by a process of “typification” as they meet increasing numbers of patients with a specific disorder and understand the key shared features of patients with that disorder, features which are unusual or atypical but still possible, and those symptoms which discount a particular diagnosis[iv]. While investigations such as blood tests and scans are often carried out, these are usually of much less help than in other areas of medicine, meaning there is less objective, biological information available to assist in making the right diagnosis.


How Reliable is Diagnosis?


For a diagnosis to be useful it must accurately describe a valid disorder and be made reliably. In the 1970s it was recognised that the reliance of psychiatry on diagnostic interview and clinical assessment without much assistance from objective biological measurements was a factor in low consistency between psychiatrists when making a diagnosis. This was particularly the case when psychiatrists were from different professional cultures or had been trained to think about mental disorders in different ways. A patient could be regarded as having a certain diagnosis by one psychiatrist, a different diagnosis by a second, and as having no disorder by a third. These problems were particularly apparent in medical research studies as without clearly defined diagnoses it was not possible to be sure that research carried out with a group of patients in one centre could be truly compared to similar research carried out in another centre.

A key development to improve reliability of diagnosis in psychiatry over the last thirty years has been the defining of specific diagnostic criteria for mental disorders in manuals published by the World Health Organisation (ICD 11 currently)[v] and the American Psychiatric Association (DSM 5)[vi]. These definitions, in combination with semi-structured interview processes carried out by carefully trained and supervised assessors, have led to much greater consistency in research studies as there are now internationally accepted diagnostic definitions allowing researchers throughout the World to be confident that they all “speak the same language”.

Away from research and academia in the real world of busy clinical practice, it is not usually possible to spend a few hours carrying out semi-structured interviews and for these interviews to be scrutinised by experienced supervisors to ensure consistency of diagnosis. There are some standardised rating instruments that can help a clinician to ensure that they have considered the key elements of the defined disorders, though the process of making a clinical diagnosis is usually a psychiatric interview as described above.

The Diagnostic and Statistical Manual (DSM) has become popular beyond the psychiatric profession and features highly in best-sellers lists whenever a new version is published. A key aspect of the appeal of these manuals is the apparent simplicity of a symptom counting process which leads to a diagnosis. However, the manual is explicitly a guide to be used by appropriately trained and experienced clinicians carefully applying judgement and must not be used like a checklist. Despite the superficial simplicity of the criteria definitions for each disorder, there remains a lot of latitude for judgement by the clinician carrying out the diagnostic assessment.  Patients showing classical or typical features of a particular mental disorder are often reliably diagnosed, however, those whose profile of symptoms and signs are unusual; closer to the boundary with other disorders, or close to normal human experience, are more likely to be given different diagnoses by different clinicians. Ultimately, much of the reliability of a diagnosis in usual clinical practice is dependent on the assessment skills of the psychiatrist.

How Valid is a Psychiatric Diagnosis?

A medical diagnosis is valid if its features make it distinct from other diagnoses and from normality, and it is associated with distress or disability. In medicine generally, there is little discussion about how valid a diagnosis is as it is usually relatively easy to distinguish different biological abnormalities from each other, and to separate a pathological condition from a variation of normal.

In psychiatry however, many diagnoses are ideas or concepts rather than biologically identifiable abnormalities. As concepts lack objective biological measurements and are much more prone to change over time and vary between cultures, the validity of psychiatric diagnoses is more open to challenge. As a result, there are frequent and sometimes heated discussions between experts and wider society about whether a particular diagnosis is valid, or even whether mental illness exists at all![vii]

There is important research being led by the National Institute of Mental Health in the USA which aims to understand more fully the basic biological and psychological abnormalities in mental disorders. This would bring the validity of psychiatric diagnoses closer to that in other areas of medicine. Hopefully, this research will create a platform for advances in care, however for now, this research has not reached a stage to use findings in clinical practice.[viii]

The standard classification systems for mental disorders that have been developed by the World Health Organisations (ICD 11) and American Psychiatric Association (DSM 5) provide an organised structure for hundreds of mental disorders with descriptions of symptoms necessary to make a diagnosis. Inclusion of a diagnosis in these systems indicates that these influential bodies regard the diagnostic concept as valid. The classification systems are revised every few years with new disorders entering the system, some leaving and some being re-defined. While often these changes are due to advancing scientific knowledge, there are other influences on the committees of experts which decide on what diagnoses to include and how these should be defined. Factors such as changes in what society regards as normal or abnormal human behaviour, changing interests and fashions in academia, and commercial pressures from drug companies or promoters of other forms of treatment can all have an influence. Therefore, what is conventionally regarded as a valid psychiatric diagnosis, and the precise definition of a diagnosis, can change over time.

Contemporary opinion is that many disorders in psychiatry are best thought of as points along a range or spectrum rather than as discrete disorders with clear boundaries from each other[ix]. Milder forms of some disorders merge with normality and so deciding whether a person’s symptoms should be given a diagnosis or not is difficult and can depend on the clinician’s own views on what is the extent of normal human mental experiences. Some influential psychiatrists have argued that the increase in diagnosis of some disorders in recent years is due to “medicalisation of normality” rather than a true increase in prevalence of mental disorders or better detection by psychiatrists[x]. Others argue that psychiatric disorders should be classified as at a particular stage depending on severity as is the case with cancer and some other disorders so that mild forms of psychiatric disorders can be identified earlier and appropriately treated[xi].

As well as unclear boundaries, many psychiatric diagnoses have symptoms which are present in several different disorders, for example, high levels of anxiety, sleep disturbance or poor concentration. This lack of specificity makes such symptoms on their own of little value in reaching a diagnosis but can be helpful in forming the overall picture needed to reach the correct diagnosis.

The definition of each disorder in diagnostic manuals such as DSM 5 or ICD 11 allows for a great range of variation, even between individuals correctly given the same diagnosis, as different symptom profiles can still satisfy standard diagnostic criteria. For example, there are 227 different combinations of symptoms and signs which can all validly meet criteria for Major Depressive Disorder, and 256 possible combinations for Borderline Personality Disorder. This means that two people with the same diagnosis can have quite different symptoms and resulting difficulties. As someone who has symptoms which satisfy one diagnostic definition will often meet criteria for one or more other diagnostic definitions at the same time, the clinician must decide whether it is best to think of an individual’s symptoms as all arising from one disorder, or whether it is better to diagnose several different disorders occurring at the same time. In clinical practice, a “principal” diagnosis is usually made which is the focus for treatment with any other diagnosed disorders regarded as “co-morbid” or “co-occurring” which influence how the principal diagnosis is manifest, though may also require treatment in addition to that for the principal diagnosis.

In some situations, particularly non-clinical or medicolegal where the presence or absence of a particular diagnosis can have great importance, there can be pressure to emphasise a particular diagnosis above others which may be equally valid.


Making a Diagnosis Useful


For a psychiatrist working in a clinical situation the central focus is providing the best care for the patient. A careful assessment should lead to a reliable and valid diagnosis (or diagnoses) that is incorporated into a formulation which explains why this person has developed this health problem at this point in their life. An assessment of the severity or stage of the disorder and details of the underlying psychological abnormalities beyond the bare bones of the diagnostic criteria of DSM or ICD further personalises the understanding of the person’s health.

A correct diagnosis allows the clinician to research what treatment interventions have been found to be helpful for other people with the same diagnosis and decide whether these would be useful for their current patient. The formulation leads to a plan to improve the person’s health using a range of interventions, including medical, psychological, social, family and lifestyle interventions.

In non-clinical situations where treatment is not the aim it is important to determine with a high degree of reliability whether a person has a mental disorder, and if so, what the diagnosis is.



Traps for Young Players


As described above, diagnosis in psychiatry may appear straightforward, though is far from it. Listed below are some common pitfalls which lead to unreliable or invalid diagnosis.


  • Making a diagnosis on inadequate information. Often it is essential to gather information from people who know the patient as well as the patient.


  • Making a diagnosis too quickly. The correct understanding of many disorders in psychiatry requires monitoring the person’s health over time. This is particularly the case in children, adolescents and young adults who are on a developmental path involving change in their mental life. It is sometimes best to keep an open mind regarding the correct diagnosis while providing the most helpful treatment meantime.


  • Using diagnostic manuals in a mechanistic, checklist, fashion rather than as references. The definitions of disorders in the diagnostic manuals are thumbnail sketches developed as an aid for experienced clinicians to improve consistency. Using the diagnostic criteria carelessly is a quick way to the wrong diagnosis or substandard treatment planning.


  • Forgetting that many diagnoses in psychiatry are concepts devised by expert committees subject to many influences in contrast to the biologically defined diagnoses in other areas of medicine. Psychiatric diagnoses are therefore more susceptible to change over time as culture and opinions in health professions and wider society change.


  • Not considering the person’s culture. Many behaviours or mental experiences which are regarded as abnormal in one culture may be normal in another. This is especially a problem when the patient and psychiatrist are from different cultural backgrounds. Though there are many international contributors, the DSM diagnostic manual as a product of the American Psychiatric Association tends to be most influenced by cultural norms in North America.


  • Being influenced, consciously or not, to reach a particular diagnosis depending on the circumstances of the assessment rather than the objectively assessed health of the person. When there are financial or other gains which could influence the clinician to reach a particular diagnosis, or not, there must be great care to avoid conscious or unconscious bias.


  • Favouring a diagnosis because the clinician has a special interest in the disorder. Clinicians with interests in a particular disorder often over-diagnose that disorder compared to their colleagues.


  • Favouring a diagnosis because the clinician specialises in or has access to treatment for a particular disorder. After all, “if all you have is a hammer everything looks like a nail”.


  • Treating the diagnosis not the person. A diagnosis is an important, though only one, element in understanding the person’s health and deciding how best to help. A formulation explains why this person has developed this health problem at this time in life and is the basis for constructing a tailored treatment plan drawing on the individual’s strengths as well as the scientific understanding of their health problem.


One Minute Summary


Correct diagnosis in psychiatry is important as this opens the door to using best research evidence to choose the most appropriate treatment.

In clinical and non-clinical situations having a particular diagnosis or not can have a large impact on a person’s life.


The lack of biological reference points makes diagnosis in psychiatry more difficult than in other areas of medicine.

In practice, the clinical interview is usually the key step in making a diagnosis.

Diagnoses can be more reliably reached by referring to standard definitions in international classification systems, though these must be used with a comprehensive understanding of psychiatry, clinical experience and good judgement.


Many diagnoses in psychiatry are concepts arising from the professional community and influenced by wider society. As such they are more susceptible to change over time than diagnoses in other areas of medicine which are based on objective biological measures.

A correct diagnosis is a crucial element in a formulation which personalises the understanding of the person’s health problems and forms the basis for a tailored treatment plan.



Further Reading and References


[i] Moynihan, R., Barratt, A.L., Buchbinder, R., Carter, S.M., Dakin, T., Donovan, J., Elshaug, A.G., Glasziou, P.P., Maher, C.G., McCaffery, K.J. and Scott, I.A., 2018. Australia is responding to the complex challenge of overdiagnosis. Medical Journal of Australia, 209(8), 332-334.

[ii] - Website address for the Centre for Using Healthcare Wisely at Bond University

[iii] “Sims' Symptoms in the Mind; Textbook of Descriptive Psychopathology” Femi Oyebode, 2018, Elsevier, – this is a general guide to understanding and describing abnormal mental experiences. A more historically interesting and philosophical text in the same area is Karl Jaspers' “General psychopathology”, Chicago University Press, January 1, 1963

[iv] Kendell, RE, 1975 “The Role of Diagnosis in Psychiatry”; Oxford, Blackwell

[v] ICD-11 International Classification of Diseases for Mortality and Morbidity Statistics Eleventh Revision; World Health Organisation, 25 May 2019

[vi] Diagnostic and Statistical Manual of Mental Disorders, 5th Edition: DSM-5, American Psychiatric Association, 2013

[vii] “Shrinks; The Untold Story of Psychiatry” Jeffrey A. Lieberman, 2015, Little, Brown and Company

[viii] For details of the project see the NIMH website -

[ix] Jablensky “Psychiatric classifications: validity and utility”, World Psychiatry, 2016 Feb;15(1):26-31

[x] “Saving Normal”, Allen Frances, 2013, HarperCollins

[xi] Clinical staging: a heuristic model for psychiatry and youth mental health. Patrick D McGorry, Rosemary Purcell, Ian B Hickie, Alison R Yung, Christos Pantelis and Henry J Jackson

Med J Aust 2007; 187 (7)

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