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Using Latent Class Analysis to Support ICD-11 Complex Posttraumatic Stress Disorder Diagnosis in a Sample of Homeless Adults

Renee Armstrong Ph.D., Lisa Phillips, MPsych, Nathan Alkemade MPsych, Meaghan O'Donnell, MPsych

June 26, 2020

Complex Posttraumatic Stress Disorder (CPTSD) is a new diagnosis that recognises that different types of traumatic experiences can impact individuals in ways that the more established diagnosis of PTSD does not capture (World Health Organization, 2018: WHO). The distinction might best be conveyed by considering the way an individual could internalise the experience of surviving a serious car accident, or terrorist attack, with the way another individual internalises repetitive childhood sexual abuse. Each survivor may experience significant difficulties with their mental health and with staying well enough to be functional in their day to day lives.

Recognising that indeed research was indicating a rethink of how we thought about the different types of symptoms related to different types of trauma, the APA decided to modify their existing PTSD diagnosis in the DSM-5, but they did not agree that the a separate diagnosis was necessary (American Psychiatric Association, 2013: APA). The ICD-11 working committee disagreed, believing that there was enough evidence to suggest that there was a distinctly different disorder that can develop as the result of prolonged, or repetitive interpersonal trauma (Maercker et al., 2013).

We investigated the CPTSD model with a group of people who have experienced homelessness and trauma in Australia. We were interested to see if this new symptom structure would help to understand the consequences of the types of trauma experienced by the individuals we interviewed. We were able to show that there were distinct differences between people who reported symptoms associated with PTSD and those who reported symptoms associated with CPTSD. However, we also found that there may be some highly trauma exposed individuals who do not fit the new model as it is currently structured. We consider why this might be the case in this particular group of people in our sample.

The concept and implementation of this new diagnosis has been in development for more than twenty years and it has generated its fair share of controversy along the way (Friedman, Resick, & Keane, 2014; Herman, 1992). There are two main manuals that are used globally to assess, diagnose and record health conditions: The International Classification of Diseases (ICD) is published by the World Health Organisation and includes all physical diseases and mental health disorders, and the 11th edition was ratified in Geneva in May 2019 (WHO, 2018). The Diagnostic and Statistical Manual (DSM), currently in its 5th edition, is published by the American Psychiatric Association (APA, 2013). This manual is exclusively dedicated to Mental Health and behavioural disorders. Each manual includes diagnostic categories that have been carefully examined by experts in the relevant area of practice and research, and where relevant and possible, field trials conducted to test the fit of a diagnosis with different groups of people. The statistical data that is generated from these diagnostic classification systems are essential for the advancement in understanding the causes and the burden of disease, in the case of the ICD, or mental health disorders in the case of both the ICD and the DSM. Updates are also critical to reflect the learning that comes back from the health professionals and researchers who use the systems to guide their work. 

However, the two manuals have some important differences as they are essentially designed for different purposes. The ICD offers a culturally diverse resource that can be utilised by clinicians in all parts of the world. This resource is valuable to many different kinds of health professionals of different types and levels of training, and is particularly important to those in remote locations. The ICD is a free, widely available multilingual resource designed to support countries to reduce the burden and mortality rates of health conditions.

The DSM, also dedicated to multicultural representation and rigorous methods of testing, offers a resource that is more prescribed and operationalised. By its third edition, the DSM revolutionized the way that mental health conditions are understood, which impacted how disorders are diagnosed and researched. The DSM remains the diagnostic system that is favored by psychiatrists and psychologists, predominately in the United States, but also in countries like Australia and Germany and is translated into multiple languages. The manual is an important revenue source for the APA and copyright permissions apply when referencing its material. The DSM is favored by mental health researchers due to the highly structured and detailed, and therefore measurable, information about how disorders are defined.

While the testing that occurs prior to new additions or adjustments to existing diagnoses in the manuals is comparable, the final presentation of the information and the process of interpretation is variable. The ICD creates some leeway for the health professional to use more clinical judgment in understanding symptoms to make a diagnosis. Given the broad use of the ICD, there is an emphasis on the bare essentials. This approach is designed to avoid complexity that might otherwise make it more difficult to fit the differences in symptoms that may occur due to the variety of settings the ICD is used in. Whereas with the DSM, clinical experience supports diagnostic interpretation, yet ultimately the requirements to meet a diagnosis is clearly defined and prescribed. In this way, the DSM could be described as more standardised, which therefore produces information that best supports scientific study. However, it is important to note that there is a strong collaborative relationship between the committees that monitor and review the manuals and in the majority of examples there is a high degree of similarity. Where there are differences, there is usually a great deal of debate, and so it is with the ICD-11’s recent inclusion of a new distinct posttrauma diagnosis of CPTSD and the APA’s decision not to include it in the DSM-5.


American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (DSM-5®): American Psychiatric Pub.

Friedman, M. J., Resick, P. A., & Keane, T. M. (2014). PTSD from DSM-III to DSM-5: Progress and challenges. In M. J. Friedman, T. M. Keane, & P. A. Resick (Eds.), Handbook of PTSD: Science and practice (Second ed.). New York: NY: The Guilford Press.

Herman, J. (1992). Trauma and recovery: The aftermath of violence-from domestic abuse to political terror. New York: Basic Books.

Maercker, A., Brewin, C. R., Bryant, R. A., Cloitre, M., Reed, G. M., van Ommeren, M., . . . Llosa, A. E. (2013). Proposals for mental disorders specifically associated with stress in the International Classification of Diseases-11. The Lancet, 381(9878), 1683-1685. doi:10.1016/S0140-6736(12)62191-6

World Health Organization. (2018). International Classification of Diseases 11th Revision: The global standard for diagnostic health information.   Retrieved from

Reference Article:

Armstrong, R. M., Philips, L., Alkemade, N., & O’Donnell, M. L. (2020 In Press). Using latent class analysis to support ICD-11 Complex Posttraumatic Stress Disorder diagnosis in a sample of homeless adults. Journal of Traumatic Stress.

Questions for Discussion

  1. Discuss implications for treatment intervention if CPTSD did not to require ‘re-experiencing’ symptoms as part of the gateway criteria.
  2. In what ways could the CPTSD diagnostic classification be most useful in:
    • a clinical formulation?
    • a research framework?
In answering question 2, consider how either the formulation or framework might look in absence of a CPTSD diagnostic classification.
  1. What are the clinical implications for the divergent diagnostic approaches the DSM-5 and the ICD-11 have taken on these symptom presentations? Explain how these might influence the approach of each classification system in the future.

About the Authors

Renée Armstrong PhD is a research fellow with Phoenix Australia| Centre for Posttraumatic Mental Health, Department of Psychiatry at the University of Melbourne and will complete her training in clinical psychology at RMIT University in 2020. Previously, Renée worked as a social worker supporting people who were experiencing homelessness. Her research has focused on capturing the mental health profile of this population, particularly in relation to trauma exposure.

Lisa Phillips MPsych (Clin) PhD is a Professor with the Melbourne School of Psychological Sciences and currently oversees the postgraduate psychology training programs offered at the University of Melbourne. She has conducted research into a broad range of issues including the development of psychotic disorders such as schizophrenia in young people, university student wellbeing and anxiety and depressive disorders. As a clinical psychologist, Lisa has worked extensively with young people and adults experiencing a wide range of mental health difficulties.

Nathan Alkemade MPsych (Clin) PhD graduated from the combined clinical masters and PhD program at the University of Melbourne and is currently a senior clinical psychologist at Monash Health. Previously, Nathan held the statistical analyst role at Phoenix Australia| Centre for Posttraumatic Mental Health where he contributed to a wide range of research projects including longitudinal investigation of psychiatric sequlea following severe injury, as well as examining diagnostic criteria changes for PTSD in both the DSM-5 and ICD-11.

Meaghan Louise O’Donnell MPsych (Clin) PhD Meaghan O’Donnell is the Head of Research at the Phoenix Australia, Centre for Posttraumatic Mental Health, and Professor in the Department of Psychiatry, University of Melbourne. She has published widely in the area of posttraumatic mental health. She is the Research Director of the Phoenix Traumatic Stress Research Clinic, which tests new and emerging treatments to promote recovery following trauma exposure. She is on a number of Australian Commonwealth scientific advisory committees. She is Past President of the International Society of Traumatic Stress Studies and is a recipient of an Experienced Researcher Humboldt Fellowship.