4 most common classes of Mental illness and their prevalence

Published on March 13, 2012


mental healthWhat is our risk of developing a mental illness over the course of our entire lives and which types of mental illnesses are we most likely to develop? These questions are not just academic in nature because the answers are of great practical importance to all of us. We need this information if we are to be prepared for its occurrence, or even prevent it from occurring. The fact is that most of us are quite likely to go through life without ever thinking about mental illness until it occurs in a family member, a friend, or ourselves. In this event we may react with surprise, shock and perhaps even anger. To be forewarned it to be forearmed.

The question of risk and type of mental illness is also important to mental health providers and governments because they need to know how frequent the various classes of mental illness are in order to effectively proportion their time, energy and money to most efficiently help individuals suffering from mental illness.


The surprising scale of the problem

Epidemiological research indicates that the probability of us experiencing a mental illness at some time in our lives is surprisingly high. For example, a recent survey of 9282 adults in the United States concluded that about half of the population will experience a mental disorder of some kind at some time in their life (Kessler et al, 2005). For the vast majority of us, this high prevalence of mental illness comes as a shock. Nevertheless we need to be aware of this surprisingly high rate of mental illness so we can prepare for its occurrence as best we can. It is also a statistic that mental health workers, community organizations, and governments around the world can use to support increased funding for mental health services and research.

What are the various ways that mental illness manifests itself and how common are each of these ways?
The Kessler (2005) study found that the four most prevalent general classes of mental illnesses, in order of decreasing rank of lifetime prevalence were anxiety disorders, impulse control disorders, mood disorders and substance use disorders.

The lifetime prevalences of each of these four general kinds of mental illness, together with a very brief description of each, is given in the table below. The lifetime prevalences range from almost 15% for substance use disorders to almost 30% for anxiety disorders.

Prevalences of top four classes of mental disorders in a recent US survey (Kessler et al, 2005)

General type of mental disorder Brief description Lifetime prevalence (%)
Anxiety disorder Characterized chiefly by anxiety in which source of anxiety is generally vague. 28.8
Impulse-control disorder Characterized by a deficit in the ability to regulate impulsive behaviour 24.8
Mood disorder Characterized by a significant disturbance in feeling state 20.8
Substance use disorde Characterized by use of psychoactive substances which would be viewed as medically harmful or socially unacceptable in almost all cultures.  14.6


Practical implications of these prevalence statistics

The Kessler study has shown that in the United States, almost half of the population is likely to experience some form of mental illness during their lifetime. This suggests that mental illness approaches physical illness in frequency of occurrence. Yet we routinely get insurance against physical illness without even thinking about mental illness.

Indeed mental illness is much less likely to be included in standard insurance policies. However the 50% probability of a mental illness occurring suggests that we should insure ourselves against both physical and mental illness and take whatever other steps we can to prepare for the situation when we or a family member succumbs to a mental illness. For example, we should better educate ourselves about how to maintain mental health and how to cope with mental illness if it does occur. We can also support the various community mental health organizations in any way we can. Finally it is to be hoped that this high prevalence of mental illness revealed by this study will help us all realize that mental illness should not be stigmatized and as something that happens to just the “defective few”.

At the present time there are no epidemiological statistics on mental disorders in Asia directly comparable to the Kessler study in the United States. However there is a yet-to-be published similar study, the Singapore Mental Health Study (SMHS; 2011), conducted by the Institute of Mental Health of Singapore covering over 6600 persons. In a media release of the preliminary results of this study, it seems that lifetime prevalence figures obtained were substantially lower than that obtained in the Kessler study. One possible explanation for this difference is that Singaporeans were more reluctant to admit to having had a mental disorder due to the greater stigmatization of mental illness in Singapore compared to the United States.


Concluding remarks

It is clear that much more epidemiological research is required to obtain reliable and accurate estimations of the prevalence of mental disorders in Asian populations. However the US study conducted by Kessler and the existing surveys conducted in Asia make it clear that the prevalences are much higher than that assumed by the vast majority of the general public. Also in order for governments to use their limited financial budgets in the most effective way, it is necessary to have better knowledge about the relative proportion of the population like to have or develop mental health problems.



Kessler, Ronald C., Berglund, Patricia, Demler, Olga, Jin, Robert, Merikangas, K. R., Walters, Ellen E., (2005). Lifetime Prevalence and Age-of-Onset Distributions of DSM-IV Disorders in the National Comorbidity Survey Replication. Archives of General Psychiatry, 62, 593-602.

The Singapore Mental Health Study (SMHS)(2011). Institute of Mental Health. Media Release. 18 November 2011.


Category(s):Addictions, Inattention, Impulsivity, & Hyperactivity (ADHD), Mood Swings / Bipolar

Written by:

Psych Mat Asia Editor

Psychology Matters Asia Editor

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