Determining how many people have a form of mental illness really depends on how a specific organization or person defines the term mental illness. Different designations of what actually constitutes a specific manifestation of mental illness will result in different estimates of the prevalence of mental illness. In the United States, the foremost organization identified with developing diagnostic criteria for different forms of mental illness is the American Psychiatric Association (APA), so this article will limit its discussion of the prevalence of mental illness to figures gathered by the APA regarding its specific designations of the different forms of mental illness. Other organizations, such as the World Health Organization (WHO), may present with different types of criteria and may have slightly different figures.
It is also important to understand that there are many critics who find the very notion of a mental illness as a socially constructed category that has no biological foundation. There is actually some relevance to this point as the majority of psychiatric diagnoses have no formal medical tests that are designed to be used in their diagnosis. Instead, mental illness is diagnosed by behavioral observations. This has led to the notion that many normal behaviors are medicalized by organizations, such as the APA, WHO, and others. Despite these controversies, the APA’s findings and diagnostic criteria still remain the most often frequently sources for diagnosing and understanding mental illness in the United States. The figures presented in this article are taken from the APA’s current Diagnostic and Statistical Manual of Mental Disorders – Fifth Edition (DSM-5) and an associated technical companion, Kaplan and Sadock’s Synopsis of Psychiatry.
It is important to note that different prevalence rates are stated for different disorders. The 12-month prevalence refers to the number or percentage of individuals who are diagnosed with a disorder in any 12-month period, whereas a lifetime prevalence rate refers to the percentage of individuals who are diagnosed with a specific disorder over their lifetime.
The figure that is typically stated is that about 26.2 percent of the American population experiences a diagnosable mental illness in a given year. Critics believe that this figure is abnormally inflated. Stated prevalence rates for select mental illnesses follow.
Prevalence by Disorder
Anxiety disorders result in the dysfunctional manifestation of fear or anxiety and related behavioral disturbances. While the experience of anxiety is common in many instances, these disorders represent the dysfunctional experience of anxiety that is either out of proportion to the situation or that does not dissipate in a normal manner. The prevalence rates for the major anxiety disorder are estimated as follows:
- Separation anxiety disorder: The 12-month prevalence rate in adults is estimated to be 0.9–1.9 percent; in children, it’s estimated to be 1.6 percent.
- Specific phobia: The 12-month prevalence rate is estimated as being between 7 percent and 9 percent.
- Social anxiety disorder (social phobia): The 12-month prevalence rate is estimated to be around 7 percent.
- Panic disorder: The 12-month prevalence rate is estimated to be 2-3 percent.
- Agoraphobia: The 12-month prevalence rate is estimated to be approximately 1.7 percent.
- General anxiety disorder: The 12-month prevalence is estimated to be 2.9 percent among adults.
Bipolar disorders are now in their own diagnostic category. There are several different types:
- Bipolar I disorder (must be diagnosed with mania): The 12-month prevalence rate is estimated at approximately 0.6 percent.
- Bipolar II disorder (diagnosis of hypomania): The 12-month prevalence rate is estimated at 0.8 percent.
- Cyclothymic disorder: This is a more chronic but less intense manifestation of bipolar-like symptoms. Lifetime prevalence is estimated to be between 0.4 percent and 1 percent.
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Depressive disorders are disorders where depression is the major feature. There are several manifestations of these disorders. The major ones are listed here.
- Major depressive disorder (clinical depression): The 12-month prevalence rate is approximately 7 percent. However, prevalence rates vary by age groups. In addition, females are diagnosed with major depressive disorder at rates that are 1.5-3 times higher than males.
- Persistent depressive disorder (a very chronic and less intense form of depression): The 12-month prevalence is estimated to be 0.5 percent.
- Premenstrual dysmorphic disorder (depression associated with the menstrual cycle): The 12-month prevalence is estimated to range between 1.8 percent and 5.8 percent.
Disruptive, Impulse Control, and Conduct Disorders
These disorders are often diagnosed in childhood. The familiar ones are listed here.
- Oppositional defiant disorder: The prevalence may vary significantly dependent on the child’s gender. It is diagnosed more commonly in males than females prior to adolescence, but this observation does not hold true in older children. The prevalence is stated as ranging from 1 percent to 11 percent, with an average prevalence estimate of 3.3 percent.
- Conduct disorder: One-year prevalence estimates range from 2 percent to 10 percent of children and adolescents. Typically, prevalence rates are higher among males than females.
- Pyromania: There appears to be no reliable population prevalence estimates available. There is one report that states lifetime prevalence as 1.13 percent; however, other disorders, such as antisocial personality disorder and bipolar disorder, were also most likely included.
- Kleptomania: The prevalence of this disorder is very rare and estimated as occurring in 0.3-0.6 percent of the adult population. Females are diagnosed with this disorder at a rate of 3:1 to males.
These are mental health disorders where there is a disruption in one’s consciousness, memory, identity, or perception.
- Dissociative identity disorder (commonly referred to as multiple personality disorder): The 12-month prevalence is estimated at 1.5 percent.
- Dissociative amnesia (a disorder associated with forgetting very important personal or autobiographical information): The 12-month prevalence is estimated at 1.8 percent.
- Depersonalization/derealization disorder (feelings of being separated from one’s body or that things are not real): Estimates of the lifetime prevalence of the disorder can range from 0.8 percent to 2.8 percent.
Feeding and Eating Disorders
This category represents the manifestation of the many familiar eating disorders.
- Anorexia nervosa (just referred to as anorexia): The 12-month prevalence in females is estimated to be 0.4 percent. The disorder is diagnosed far less often in males, and the prevalence in males is not known. It is suggested that the disorder is diagnosed at a ratio of 10:1 for females to males.
- Bulimia nervosa (often referred to as bulimia): The 12-month prevalence in females is estimated to be between 1 percent and 1.5 percent. Again, the prevalence in males is not stated, but it is stated that the diagnosis occurs at a 10:1 female-to-male ratio.
- Binge eating disorder: The 12-month prevalence in females is 1.6 percent and in males 0.8 percent.
This disorder is commonly referred to in other contexts as gender identity disorder. The diagnostic criteria for these disorders are markedly different for children and adults, and prevalence rates differ depending on these factors and on one’s biological gender. The prevalence rates are quite small. For adult males, the prevalence ranges between 0.005 percent and 0.014 percent, and for biological females, from 0.002 percent to 0.003 percent. Estimates for prevalence in children are not stated.
Obsessive-Compulsive and Related Disorders
Previously, these disorders were listed as anxiety disorders, but in the DSM-5, they have their own category. The most familiar disorders are listed here.
- Obsessive-compulsive disorder: The 12-month prevalence is estimated at 1.2 percent.
- Body dysmorphic disorder (a disorder where an individual has unrealistic preoccupation with a perceived deficit or flaw in their appearance that is not noticeable to others): The prevalence is estimated at around 2.4 percent with minor variations in males and females. In cosmetic surgery patients, the prevalence is significantly higher.
- Hoarding disorder: While the prevalence of this disorder is not well defined, estimates indicate these prevalence rates are between 2 percent and 6 percent. The disorder may be more prevalent in older individuals and may be three times more common in individuals 55 years or older compared to younger individuals.
- Trichotillomania (hair pulling disorder): The 12-month prevalence estimate is between 1 percent and 2 percent. Females are diagnosed at a rate of 10:1 to males.
- Excoriation disorder (skin picking): Lifetime prevalence in adults is 1.4 percent.
These disorders represent the obtainment of sexual excitement through atypical means. There are number of these disorders; some the most well-known are listed here.
- Voyeuristic disorder (sexual arousal from observing others in compromising or sexually explicit situations): Estimates of lifetime prevalence suggest that is 12 percent in males and 4 percent in females.
- Exhibitionistic disorder: The estimate in males is 2-4 percent, and it is much lower in females.
- Frotteuristic disorder (getting sexual arousal from touching or rubbing against non-consenting individuals): Estimates of prevalence of the disorder are difficult to find, but suggest that 30 percent of adult males perform this type of behavior at one time or another. Simply occasionally engaging in the behavior is not diagnosable as a disorder.
- Sexual masochisms disorder: The 12-month prevalence in Australia is estimated at 2.2 percent of males and 1.3 percent of females. Estimates in the US are unknown.
- Sexual sadism disorder: Estimates vary widely depending on the context (2-30 percent).
- Pedophilic disorder: Estimates are unknown but the highest possible prevalence in males is considered to be 3-5 percent, and the prevalence in females is probably a fraction of this.
- Transvestite disorder: This disorder is extremely rare (being sexually aroused by wearing clothes of the opposite gender). Fewer than 3 percent of males report ever participating in this behavior; however, the prevalence of the disorder as a result of engaging in this behavior is not stated in the DSM-5.
For the 10 personality disorders, the estimated prevalence rates are outlined below.
- Paranoid personality disorder: Estimates of prevalence range from 2.3 percent to 4.4 percent.
- Schizoid personality disorder: The estimated prevalence is around 3.1 percent.
- Schizotypical personality disorder: Estimates vary and appear to be higher in the general population than in clinics. The estimate for the general population is around 3.9 percent.
- Antisocial personality disorder: The 12-month prevalence rate is estimated between 0.2 percent and 3.3 percent. Men are diagnosed with the disorder at a much higher rate than women.
- Borderline personality disorder: Median population prevalence is estimated at between 1.6 percent and 5.9 percent. Females receive this diagnosis significantly more often than males.
- Histrionic personality disorder: The prevalence estimate is 1.84 percent.
- Narcissistic personality disorder: Estimates vary substantially and range between near 0 percent to 6.2 percent in community samples.
- Avoidant personality disorder: Estimates of the prevalence fall around 2.4 percent.
- Dependent personality disorder: Estimates range from 0.49 percent to 0.6 percent.
- Obsessive-compulsive personality disorder: Estimates range from 2.1 percent to 7.9 percent.
Schizophrenia and Related Psychotic Disorders
These disorders share a number of different psychotic features, including the presence of hallucinations, delusions, disorganized or abnormal behaviors, disorganized thinking, disorganized speech, and negative symptoms, such as the inability to experience pleasure (anhedonia), a lack of emotion (abulia), a lack of motivation (avolution), and a number of other manifestations.
- Brief psychotic disorder (the experience of psychotic episodes for at least one day but less than one month): The prevalence is not reported, but it is reported that brief psychotic disorder may account for 9 percent of all new reported cases of psychotic behavior in individuals.
- Schizophrenia: The lifetime prevalence is generally estimated to be between 0.3 percent and 0.7 percent; however, a number of factors may affect this, including gender and ethnic background.
- Schizoaffective disorder (schizophrenia-like symptoms with depression or mania): The lifetime prevalence is estimated to be around 0.3 percent.
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These are disorders of the sleep cycle. The most well-known are included here.
- Insomnia disorder: The prevalence of this disorder varies depending on how it is defined; however, 6-10 percent of the population appears to meet the criteria for this disorder.
- Hypersomnolence disorder (excessive sleepiness): Estimates indicate that about 1 percent of the population has this disorder.
- Narcolepsy: Estimates of the prevalence indicate that 0.02-0.04 percent of the population have this disorder.
- Obstructive sleep apnea: Estimates vary based on age. It is estimated that at least 1-2 percent of children, 2-15 percent of middle-aged adults, and greater than 20 percent of older adults meet the criteria for this disorder. Males appear to be diagnosed with this disorder 2-4 times more often than females.
- Restless leg syndrome: Estimates of this disorder range from 2 percent to 7.2 percent.
Somatic Symptom and Related Disorders
This group of disorders includes disorders formally categorized as meditation disorders. The better known of these disorders are listed here.
- Conversion disorder (the presence of neurological symptoms, such as blindness or paralysis without any physical cause): Transient conversion symptoms are actually rather common but the actual prevalence of this disorder is not well known. It appears that the incidence of persistent conversion symptoms that would lead to a diagnosis of this disorder are extremely rare and estimated to occur at 2-5/100,000 or between 0.00002 percent and 0.00005 percent a year.
- Factitious disorder (faking psychological signs or symptoms without any real disorder): The actual prevalence is unknown; however, the context would certainly affect the prevalence. For instance, individuals suing for slip and fall or other types of issues will have higher prevalence rates. It is estimated that about 1 percent of individuals have presentations that meet the criteria for this disorder.
- Somatic symptom disorder (having obsessive behaviors associated with physical symptoms): The prevalence is estimated to be around 5-7 percent with females having higher prevalence rates than males.
- Illness anxiety disorder (formally referred to as hypochondriasis): Prevalence estimates range from 1.3 percent to 10 percent.
Substance Use Disorders
These are categorized by type.
- Alcohol use disorder: The 12-month prevalence is estimated to be 4.6 percent among individuals who are 12-17 years old and 8.5 percent in adults over the age of 18. Rates differ depending on gender, age, and ethnic background. For example, the 12-month prevalence for individuals between the ages of 18 and 29 is 16.2 percent, whereas it is 1.5 percent in individuals over 65 years of age. Rates of the disorder are higher in adult males (12.4 percent) compared to adult females (4.9 percent). Prevalence rates are also affected by ethnic background.
- Cannabis use disorder: The 12-month prevalence rates are reported as being approximately 3.4 percent among individuals between the ages of 12 and 17 and 1.5 percent among adults over the age of 18. Males are diagnosed with cannabis use disorders at higher rates than females (2.2 percent for males compared to 0.8 percent for females).
- Other hallucinogen use disorder. The DSM has a special category for PCP use disorder; however, the prevalence of this disorder is unknown. Other hallucinogen use disorder refers to substance use disorders to other hallucinogenic drugs. Twelve-month prevalence rates are estimated to be 0.5 percent for individuals 12-17 and 0.1 percent for individuals over 18 years old.
- Inhalant use disorder: The 12-month prevalence appears to be around 0.4 percent of individuals between the ages of 12 and 17 years old. For individuals over the age of 18, the prevalence appears to be about 0.1 percent.
- Opioid use disorder: Obviously, prevalence will vary depending on the particular opioid drug. The 12-month prevalence for opioid use disorders among adults is estimated to be 0.37 percent.
- Sedative, hypnotic, or anxiolytic use disorder (contains drug such as benzodiazepines, barbiturates, sleeping pills, etc.): The prevalence rates are stated as being unclear, but it is also stated that 2.2 percent of Americans over 12 years of age use these drugs.
- Stimulant use disorder (includes drugs like Ritalin, cocaine, methamphetamine, and other stimulants): The 12-month prevalence for cocaine use disorder is estimated at 0.2 percent for individuals ages 12-17 and 0.3 percent for individuals over the age of 18. The 12-month prevalence for amphetamine type use disorders is estimated to be 0.2 percent among all age groups.
- Tobacco use disorder: The 12-month prevalence rate is 13 percent of adults in the United States.
- Gambling disorder (although not a formal substance use disorder, considered to be a type of addiction): The lifetime prevalence rate is between 0.4 percent and 1 percent. It appears to be three times more common in males than females and about twice as common in African Americans than in Caucasians.