Evidence Basis for Psychological Disorder Classification


A trained mental health professional will use interviews, psychometric tests, background information to be able to make a diagnosis of a psychological disorder. (Weekly 3, Weekly notes). A diagnosis is formed by comparing the data that has been gathered to that of the Diagnostic and Statistical Manual of Mental Disorder (APA, 2013) or the International Classification of Diseases (WHO, 1992). These manuals are both used in the classification of psychological disorders and requires the clinician to make judgments on each of the five axes. The DSM classification system lists 16 categories of disturbance and more than 200 subcategories. Abnormal behaviour classification is made on the basis of Axis I (Clinical Syndromes) and Axis II (Personality Disorders). The other three axes are used as supplementary information — Axis III (General Medical Conditions), Axis IV (Psychosocial and Environmental Problems), and Axis V (Global Assessment of Functioning)—are used to provide supplementary information. (APA, 2013)

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Clarke et al (1995) describe comorbidity as the co-occurrence of two more disorders in the same individual. Comorbidity occurs when an individual meets diagnostic criteria for more than one disorder or has symptoms from multiple disorders even if they occur at a subclinical level (Kazdin 2005). Clinicians need to consider these problems as part of a whole complex of phenomena that are closely linked to one another and not deal with each disorder separately.( DOHA, 2008)

Strong Evidence Base: Personality Disorders

Key features of Personality Disorders are distorted thinking patterns, problematic emotional responses, unregulated impulse control and interpersonal difficulties. These can blend in various ways to form ten specific personality disorders identified in DSM-5 (APA, 2013) and are grouped in 3 clusters which are:

Cluster A- social awkwardness and social withdrawal that are dominated by distorted thinking

Paranoid Personality Disorder
Schizoid Personality Disorder
Schizotypal Personality Disorder

Cluster B- problems with impulse control and emotional regulation

Borderline Personality Disorder
Narcissistic Personality Disorder
Histrionic Personality Disorder
Antisocial Personality Disorder

Cluster C- high level of anxiety

Avoidant Personality Disorder
Dependent Personality Disorder
Obsessive-Compulsive Personality Disorders.

In order to be diagnosed with a specific personality disorder an individual must meet the minimum criteria with symptoms that cause distress and functional impairment.

Research suggests that personality disorders frequently co-occur with each other and with other disorders such as:

Bipolar Disorder
Social Phobia
Substance Use Disorders
Eating Disorders

About half of all people who meet the criteria for one personality disorder will also meet the criteria for at least one other (Fowler, O’Donohue & Lilienfeld, 2007). Studies on the prevalence of personality disorders performed in different countries and amongst different populations suggest that roughly 10% of adults can be diagnosed with a personality disorder (Torgersen, 2005). There is sufficient research and empirical evidence to support the symptoms, diagnostic instruments and treatment for personality disorder.

Weak Evidence Base: Anxiety Disorders

Key features of Anxiety Disorders are mental apprehension, physical tension, physical symptoms and dissociative anxiety, restlessness or nervousness, easy fatigability, poor concentration, irritability, muscle tension, or sleep disturbance. (Healy, 2008). In anxiety disorders, culture plays a significant role with a wide range of what is acceptable and normative. DSM-5 (APA, 2013) classify anxiety disorders into the following categories

Panic disorder
Social Anxiety Disorder
Specific Anxiety Disorder.
Separation Anxiety Disorder
Selective Mutism
Generalized Anxiety Disorder
Post-Traumatic Stress Syndrome

In order to be diagnosed with a specific anxiety disorder an individual must meet the minimum criteria with symptoms that cause distress and significant problems in their functioning.

Anxiety is a normal human emotion but can also be a symptomatic feature of many different psychiatric disorders such as:

Avoidant Personality Disorder
Mood Disorder/ Depression
Schizophrenia Spectrum Disorders
Substance Use Disorders

Anxiety disorders are fairly common with approximately 18% of the American population experiencing an anxiety in a year (NIMH, 2008). Each disorder is applicable to both children and adults with an average onset of 21.5 years of age. The presence of some anxiety symptoms does not automatically indicate an anxiety disorder. (Jacofsky et al,

DSM-5 (APA, 2013) acknowledges that the overlap of anxiety disorders may represent alternative conceptualizations of the same or similar conditions and more research is needed to identify differences. It may also be difficult to separate anxiety from depression when both disorders co-occur resulting in poorer response to treatment. There is inconsistent evidence on comorbidity of schizophrenia and anxiety. Some studies suggest that having both disorders has no significant effect. Other research points to poorer outcomes when both disorders are present (Pokos & Castle, 2006).

Reasons for Difference in Evidence Base

Clark et al (1995) discusses that some disorders are currently placed in the wrong diagnostic class e.g. should be listed as a dissociative disorder rather than an anxiety disorder. They suggest that this presents a taxonomic problem for which no solution has been found. Another problem isheterogeneity. Most research is focussed on a limited range of disorders with researchers not being aware of similar issues in the discipline as a whole.( Week 4, Weekly Notes) Individuals could be relatively dissimilar to each other and have very little in common but may get classified into the same diagnostic group. Psychometric tests used may not be relevant across different cultural or age groups.


To be able to determine the appropriate treatment process, Clinicians must be able to determine the psychologically sound diagnosis based on the evidence available and the diagnostic criteria set out in the DSM-5 or ICD-10. Interrelated groups of diagnoses make this a complex and demanding task.


American Psychiatric Association. (APA) (2013)Diagnostic and Statistical Manual of Mental Disorders(5th edn) (DSM-5)

Clark, L. A., Watson, D., & Reynolds, S. (1995). Diagnosis and classification of psychopathology: Challenges to the current system and future directions.Annual Review of Psychology,46, 121–153.

Department of Health and Ageing (DOHA) (2008) Comorbidity of mental disorders and substance use: A brief guide for the primary care clinician. Retrieved September 3rd 2014 from Drug and Alcohol Services South Australia website: www.nationaldrugstrategy.gov.au/internet/drugstrategy/…/mono71.pdf

Fowler, K.A., O’Donohue, W., Lilienfeld, S.O. (2007). Introduction: Personality Disorders In Perspective. In O’Donohue, W.T., Fowler, K.A., Lilienfeld, S.O. (Eds.). Personality Disorders: Toward the DSM V. Thousand Oaks: Sage Publications.

Healy, D. (2008) Drugs Explained, Section 5: Management of Anxiety, Elsevier Health Sciences, 2008, pp. 136–137

Jacofsky, M.D., Santos, M.T., Khemlani-Patel, S., Neziroglu, F. (2014) Anxiety and Other Psychiatric Disorders. Retrieved September 2nd 2014 from Seven Counties Services website: http://www.sevencounties.org/poc/view_doc.php?type=doc&id=38463&cn=1

Kazdin AE. 2005. Evidence-based assessment for children and adolescents: issues in measurement development and clinical applications.Journal of. Clinical Child & Adolescent Psychology. 34:548–58

Laureate Online Education (2011) Week 3, Weekly notes: Assessments in mental health continued https://elearning.uol.ohecampus.com/bbcswebdav/institution/UKL1/MAP/201480_AUGUST/APPTRE/readings/APPTRE_Week03_weeklyNotes.html

Laureate Online Education (2011) Week 4, Weekly notes: Diagnoses and case formulation. https://elearning.uol.ohecampus.com/bbcswebdav/institution/UKL1/MAP/201480_AUGUST/APPTRE/readings/APPTRE_Week04_weeklyNotes.html

National Institute of Mental Health (2008). Statistics. The numbers count: Mental disorders in America. Retrieved September 3rd 2014 from NIMH website http://www.nimh.nih.gov/statistics/index.shtml

Pokos, V., & Castle, D. J. (2006). Prevalence of comorbid anxiety disorders in schizophrenia spectrum disorders: A literature review. Current Psychiatry Review 2, 285-307.

Torgersen, S. (2005). Epidemiology. In Oldham, J.M., Skodol, A.E., Bender, D. S (Eds.). The American Psychiatric Publishing Textbook of Personality Disorders (pp. 129-143). Washington, D.C.: American Psychiatric Publishing.

World Health Organization (WHO) (1992). International classification of diseases (ICD-10). Geneva, Switzerland: Author.

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