Diagnosing and Classifying Mental Disorders

Learning Objectives

  • Describe the basic features of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) and how it is used to classify disorders
  • Outline the major disorder categories of the DSM-5

A first step in the study of mental disorders is carefully and systematically discerning significant signs and symptoms. How do mental health professionals ascertain whether or not a person’s inner states and behaviors truly represent a psychological disorder? Arriving at a proper diagnosis—that is, appropriately identifying and labeling a set of defined symptoms—is absolutely crucial. This process enables professionals to use a common language with others in the field and aids in communication about the disorder with the patient, colleagues, and the public. A proper diagnosis is an essential element to guide proper and successful treatment. For these reasons, classification systems that organize psychological disorders systematically are necessary.

Diagnostic and Statistical Manual of Mental Disorders (DSM-5)

Although a number of classification systems have been developed over time, the one that is used by most mental health professionals in the United States is the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), published by the American Psychiatric Association in 2013. Additions and revisions were made in March 2022, so the most current edition is called the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR). (Note that the American Psychiatric Association differs from the American Psychological Association; both are abbreviated APA.) This textbook includes the updates from the DSM-5-TR, though we typically continue to reference the diagnostic manual simply as the DSM-5.

The first edition of the DSM, published in 1952, classified psychological disorders according to a format developed by the U.S. Army during World War II (Clegg, 2012). In the years since, the DSM has undergone numerous revisions and editions. The DSM-5 includes many categories of disorders (e.g., anxiety disorders, depressive disorders, and dissociative disorders). Each disorder is described in detail, including an overview of the disorder (diagnostic features), specific symptoms required for diagnosis (diagnostic criteria), prevalence information (what percent of the population is thought to be afflicted with the disorder), and risk factors associated with the disorder. Figure 1 shows lifetime prevalence rates—the percentage of people in a population who develop a disorder in their lifetime—of various psychological disorders among U.S. adults. These data were based on a national sample of 9,282 U.S. residents (National Comorbidity Survey, 2007).

A bar graph has an x-axis labeled “DSM disorder” and a y-axis labeled “Lifetime prevalence rates.” For each disorder, a prevalence rate is given for total population, females, and males. Appropriate alternative text can be found in the data table displayed below this image. The approximate data shown is: “major depressive disorder” 17% total, 20% females, 13% males; “alcohol abuse” 13% total, 7% females, 20% males; “specific phobia” 13% total, 16% females, 8% males; “social anxiety disorder” 12% total, 13% females, 11% males; “drug abuse” 8% total, 5% females, 12% males; “posttraumatic stress disorder” 7% total, 10% females, 3% males; “generalized anxiety disorder” 6% total, 7% females, 4% males; “panic disorder” 5% total, 6% females, 3% males; “obsessive-compulsive disorder” 3% total, 3% females, 2% males; “dysthymia” 3% total, 3% females, 2% males.

Figure 1. The graph shows the breakdown of psychological disorders, comparing the percentage prevalence among adult males and adult females in the United States. Because the data is from 2007, the categories shown here are from the DSM-4, which has been supplanted by the DSM-5. Most categories remain the same; however, alcohol abuse now falls under a broader alcohol use disorder category.

Table 1. DSM Disorder Lifetime Prevalence Rates
DSM Disorder Total Females Males
Major Depressive Disorder 17% 20% 13%
Alcohol Abuse 13% 7% 20%
Specific Phobia 13% 16% 8%
Social Anxiety Disorder 12% 13% 11%
Drug Abuse 8% 5% 12%
Post-Traumatic Stress Disorder 7% 10% 3%
Generalized Anxiety Disorder 6% 7% 4%
Panic Disorder 5% 6% 3%
Obsessive-Compulsive Disorder 3% 3% 2%
Persistent Depressive Disorder 3% 3% 2%

More recent data shows that the most prevalent disorders at any given time (not over a lifetime) are anxiety disorders, as shown in the following chart.[1]

Prevalence by mental and substance use disorder (2017). Data shows anxiety disorders as most prevalent at 6.64%, depression 4.84%, drug use 3.45%, alcohol use at 2.04%, bipolar 0.65%, eating disorders 0.51%, and schizophrenia 0.33%.

Figure 2. The prevalence of mental and substance use disorders in the United States.

The DSM-5 also provides information about comorbidity; the co-occurrence of two disorders. For example, the DSM-5 mentions that 41% of people with obsessive-compulsive disorder (OCD) also meet the diagnostic criteria for major depressive disorder (Figure 2). Drug use is highly comorbid with other mental illnesses; six out of 10 people who have a substance use disorder also suffer from another form of mental illness (National Institute on Drug Abuse [NIDA], 2007).

A Venn-diagram shows two overlapping circles. One circle is titled “Obsessive-Compulsive Disorder” and the other is titled “Major Depressive Disorder.” The area in which these two circles overlap includes forty-one percent of each circle. This area is titled “Comorbidity 41%.”

Figure 3. Obsessive-compulsive disorder and major depressive disorder frequently occur in the same person.


Co-occurrence and comorbidity of psychological disorders are quite common, and some of the most pervasive comorbidities involve substance use disorders that co-occur with psychological disorders. Indeed, some estimates suggest that around a quarter of people who suffer from the most severe cases of mental illness exhibit substance use disorder as well. Conversely, around 10 % of individuals seeking treatment for substance use disorder have serious mental illnesses. Observations such as these have important implications for treatment options that are available. When people with a mental illness are also habitual drug users, their symptoms can be exacerbated and resistant to treatment. Furthermore, it is not always clear whether the symptoms are due to drug use, the mental illness, or a combination of the two. Therefore, it is recommended that behavior is observed in situations in which the individual has ceased using drugs and is no longer experiencing withdrawal from the drug in order to make the most accurate diagnosis (NIDA, 2018).

Obviously, substance use disorders are not the only possible comorbidities. In fact, some of the most common psychological disorders tend to co-occur. For instance, more than half of individuals who have a primary diagnosis of depressive disorder are estimated to exhibit some sort of anxiety disorder. The reverse is also true for those diagnosed with a primary diagnosis of an anxiety disorder. Further, anxiety disorders and major depression have a high rate of comorbidity with several other psychological disorders (Al-Asadi, Klein, & Meyer, 2015).

The DSM has changed considerably in the half-century since it was originally published. The first two editions of the DSM, for example, listed homosexuality as a disorder; however, in 1973, the APA voted to remove it from the manual (Silverstein, 2009). While the DSM-3 did not list homosexuality as a disorder, it introduced a new diagnosis, ego-dystonic homosexuality, which emphasized homosexual arousal that the patient viewed as interfering with desired heterosexual relationships and causing distress for the individual. This new diagnosis was considered by many as a compromise to appease those who viewed homosexuality as a mental illness. Other professionals questioned how appropriate it was to have a separate diagnosis that described the content of an individual’s distress. In 1986, the diagnosis was removed from the DSM-3-R (Herek, 2012).

WAtch It

This video provides an overview of some of the history related to the development and evolution of the DSM.

You can view the transcript for “We Were Super Wrong About Mental Illness: The DSM’s Origin Story” here (opens in new window).

Additionally, beginning with the DSM-3 in 1980, mental disorders have been described in much greater detail, and the number of diagnosable conditions has grown steadily, as has the size of the manual itself. DSM-1 included 106 diagnoses and was 130 total pages, whereas DSM-3 included more than twice as many diagnoses (265) and was nearly seven times its size (886 total pages) (Mayes & Horowitz, 2005). Although DSM-5 is longer than DSM-4, the volume includes only 237 disorders, a decrease from the 297 disorders that were listed in DSM-4. The DSM-5, includes revisions in the organization and naming of categories and in the diagnostic criteria for various disorders (Regier, Kuhl, & Kupfer, 2012), while emphasizing careful consideration of the importance of gender and cultural difference in the expression of various symptoms (Fisher, 2010). The most recent

Some believe that establishing new diagnoses might over-pathologize the human condition by turning common human problems into mental illnesses (The Associated Press, 2013). Indeed, the finding that nearly half of all Americans will meet the criteria for a DSM disorder at some point in their life (Kessler et al., 2005) likely fuels much of this skepticism. The DSM-5 is also criticized on the grounds that its diagnostic criteria have been loosened, thereby threatening to “turn our current diagnostic inflation into diagnostic hyperinflation” (Frances, 2012, para. 22). For example, DSM-4 specified that the symptoms of major depressive disorder must not be attributable to normal bereavement (loss of a loved one). The DSM-5, however, removed this bereavement exclusion, essentially meaning that grief and sadness after a loved one’s death can constitute major depressive disorder.

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Categories in the DSM

The DSM-5 is divided into 22 chapters that include sets of related disorders. This organization is evident in every chapter so that related disorders appear closer to each other, and psychological and biological diseases often relate to each other. However, if an illness that is primarily medical is not specified in DSM-5, clinicians may use the current ICD diagnoses to specify the condition. 

Link to Learning

View the DSM-5 Table of Contents here. Note that the overall outline is the same in the DSM-5-TR, though the contents and some of the language have changed slightly. For example, “dysthymia” is no longer used to describe “persistent depressive disorder,” the terminology for “intellectual disability” has been replaced with “intellectual development disorder” and “conversion disorder” is better known as “functional neurological symptom disorder.” A new disorder, prolonged grief disorder, was added to the section on trauma- and stressor-related disorders.

The current organization of the DSM-5 begins with neurodevelopmental disorders and then proceeds through internalizing problems (depression, anxiety, social anxiety, somatic complaints, post-traumatic symptoms, and obsession-compulsion) to externalizing problems (disruptive, impulse-control, conduct disorders and substance use, etc.). [2]

We have organized this course according to the DSM-5 and devote time in each of the modules to discuss the main features of mental disorders from each of the DSM-5 categories. Throughout these modules, you will learn the basic diagnostic criteria, the etiology (causes), epidemiology (prevalence), and treatment options for each category of disorders. In this way, you can gain a basic understanding of each category of mental disorders, including all of the following:

  1. neurodevelopmental disorders
  2. schizophrenia spectrum and other psychotic disorders
  3. bipolar and related disorders
  4. depressive disorders
  5. anxiety disorders
  6. obsessive-compulsive and related disorders
  7. trauma- and stressor-related disorders
  8. dissociative disorders
  9. somatic symptom and related disorders
  10. feeding and eating disorders
  11. elimination disorders
  12. sleep-wake disorders
  13. sexual dysfunctions
  14. gender dysphoria
  15. disruptive, impulse-control, and conduct disorders
  16. substance-related and addictive disorders
  17. neurocognitive disorders
  18. personality disorders
  19. paraphilic disorders
  20. Other mental disorders[3]

Overview of the Major Disorder categories

In this course, the major disorders categories begin with anxiety disorders. Any anxiety or fear that interferes with normal functioning may be classified as an anxiety disorder. Commonly recognized categories include specific phobias: a specific unrealistic fear; social anxiety disorder: extreme fear and avoidance of social situations; panic disorder: suddenly overwhelmed by panic even though there is no apparent reason to be frightened; agoraphobia: an intense fear and avoidance of situations in which it might be difficult to escape; and generalized anxiety disorder: a relatively continuous state of tension, apprehension, and dread. 

Another module deals with obsessive-compulsive and related disorders and trauma- and stressor-related disorders. While similar to anxiety disorders, obsessive-compulsive disorders and posttraumatic stress disorders now have their own distinct categories of classification within the DSM-5 because symptoms of anxiety are not necessarily present. With obsessive-compulsive disorder, a person is obsessed with unwanted, unpleasant thoughts and/or compulsively engages in repetitive behaviors or mental acts, perhaps as a way of coping with the obsessions. Post-traumatic stress disorder is a similar disorder, although classified as a trauma- and stressor-related disorder.

Link to Learning

Learn more about each of the psychological disorders through the National Institute of Mental Health.

Or for an interesting application of the various mental disorders, take a look at this YouTube playlist showing disorders as they are characterized in popular media. These case studies were developed by students in Dr. Caleb Lack’s psychology class.

Post-traumatic stress disorder is a disorder in which the experience of a traumatic or profoundly stressful event, such as combat, sexual assault, or natural disaster, produces a constellation of symptoms that must last for one month or more. These symptoms include intrusive and distressing memories of the event, flashbacks, avoidance of stimuli or situations that are connected to the event, persistently negative emotional states, feeling detached from others, irritability, proneness toward outbursts, and a tendency to be easily startled.

In another module, we discuss dissociative disorders, somatic symptom, and related disorders. The main characteristics of dissociative disorders are that people become dissociated from their sense of self, resulting in memory and identity disturbances. Dissociative disorders listed in the DSM-5 include dissociative amnesia, depersonalization/derealization disorder, and dissociative identity disorder. A person with dissociative amnesia is unable to recall important personal information, often after a stressful or traumatic experience. Depersonalization/derealization disorder is characterized by recurring episodes of depersonalization (i.e., detachment from or unfamiliarity with the self) and/or derealization (i.e., detachment from or unfamiliarity with the world). A person with dissociative identity disorder exhibits two or more well-defined and distinct personalities or identities, as well as memory gaps for the time during which another identity was present. Dissociative identity disorder has generated controversy, mainly because some believe its symptoms can be faked by patients if presenting its symptoms somehow benefits the patient in avoiding negative consequences or taking responsibility for one’s actions. The diagnostic rates of this disorder have increased dramatically following its portrayal in popular culture. However, many people legitimately suffer over the course of a lifetime with this disorder.

Somatic symptom disorders were previously known as “somataform disorders.” These include somatic symptom disorder, illness anxiety disorder, functional neurological symptom disorder (conversion disorder), and fictitious disorder. You will read about the various symptoms, epidemiology, how individuals present with these problems, and a brief overview of possible causes. These disorders relate to a person experiencing physical ailments that are not fully explained by a medical condition.

Mood disorders are discussed in another module. A mood disorder involving unusually intense and sustained sadness, melancholia, or despair is known as major depressive disorder. Milder but still prolonged depression can be diagnosed as persistent depressive disorder. Bipolar disorder is characterized by mood states that vacillate between sadness and euphoria; a diagnosis of bipolar disorder requires experiencing at least one manic episode, which is defined as a period of extreme euphoria, irritability, and increased activity. Mood disorders appear to have a genetic component, with genetic factors playing a more prominent role in bipolar disorder than in depression. Both biological and psychological factors are important in the development of depression. People who suffer from mental health problems, especially mood disorders, are at heightened risk for suicide.

Next, we discuss feeding and eating disorders. Disordered eating can have significant health consequences, and eating disorders are a major health concern. Anorexia nervosa is an eating disorder characterized by the maintenance of a bodyweight well below average through starvation and/or excessive exercise. Individuals suffering from anorexia nervosa often have a distorted body image, referenced in literature as a type of body dysmorphia, meaning that they view themselves as overweight even though they are not. People suffering from bulimia nervosa engage in binge eating behavior that is followed by an attempt to compensate for a large amount of consumed food. Avoidant/restrictive food intake disorder is an eating or feeding disturbance associated with an apparent lack of interest in eating or food. Pica is a disorder characterized by an appetite for substances that are largely non-nutritive, such as ice, soap, hair, paper, metal, soil, stones, glass, or chalk.

Many people experience disturbances in their sleep at some point in their lives. Sleep-wake disorders involve problems with the quality, timing, and amount of sleep, which result in daytime distress and impairment in functioning. Sleep-wake disorders often occur along with medical conditions or other mental health conditions, such as depression, anxiety, or cognitive disorders.

Substancerelated disorders are discussed in a separate module. They result when a craving for, the development of, a tolerance to, and difficulties in controlling the use of a particular substance or a combination of different substances, as well as withdrawal syndromes when a person ceases to use the substance(s). Other addictive disorders also include gambling disorder and other behavioral addictions.

Next, we cover the topics of gender dysphoria, paraphilic disorders, and sexual dysfunctions. Today more than ever before, mental health professionals are seeing patients seeking treatment in response to dissatisfaction with their sexual functioning. Such dissatisfaction most commonly stems from a sexual dysfunction, but may also be the result of a sexual deviation. Sexual dysfunction disorders include sexual desire disorders, arousal disorders, orgasm disorders, and pain disorders. From a clinical perspective, there has been some effort to define sexual deviation under the umbrella of sexual paraphilias. Dissatisfaction can also stem from gender dysphoria, or the distress a person feels due to a mismatch between their gender identity and their sex assigned at birth.

The DSM-5 classifies psychotic disorders that involve psychosis, or a break in reality, like in schizophrenia, delusional disorder, brief psychotic disorder, schizophreniform disorder, schizoaffective disorder, substance/medication-induced psychotic disorder, and psychotic disorder due to another medical condition. The most common psychotic disorder in this domain is schizophrenia, which is a severe disorder characterized by delusions and hallucinations, often causing a breakdown in one’s ability to function in life.

The DSM-5 recognizes 10 personality disorders, organized into three clusters. The disorders in Cluster A include those characterized by a personality style that is odd and eccentric. These include paranoid, schizoid, and schizotypal personality disorders. Cluster B includes personality disorders characterized chiefly by a personality style that is impulsive, dramatic, highly emotional, and erratic (antisocial, histrionic, narcissistic, and borderline), and those in Cluster C are characterized by a nervous and fearful personality style (avoidant, dependent, and obsessive-compulsive).

Neurodevelopmental disorders are covered in another module, along with elimination disorders and disruptive, impulse-control, and conduct disorders. The neurodevelopmental disorders are a group of disorders that are typically diagnosed during childhood and are characterized by developmental deficits in personal, social, academic, and intellectual realms; these disorders include attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder. The major features of autism spectrum disorder include deficits in social interaction and communication and repetitive movements or interests. ADHD is characterized by a pervasive pattern of inattention and/or hyperactive and impulsive behavior that interferes with normal functioning. Genetic and neurobiological factors contribute to the development of ADHD, which can persist well into adulthood and is often associated with poor, long-term outcomes. 

Disruptiveimpulsecontrol, and conduct disorders refer to a group of disorders that include oppositional defiant disorder, conduct disorder, intermittent explosive disorder, kleptomania, and pyromania. These disorders can cause people to behave angrily or aggressively toward people or property.

Finally, we learn about neurocognitive disorders—disorders that describe decreased mental function due to a medical disease other than a psychiatric illness. It is often used synonymously (but incorrectly) with dementia. Although Alzheimer’s disease accounts for the majority of cases of neurocognitive disorders, several other conditions can similarly affect memory, thinking and reasoning, and the motor system. In addition to Alzheimer’s, these conditions include frontotemporal degeneration, Huntington’s disease, Lewy body disease, traumatic brain injury (TBI), Parkinson’s disease, prion disease, and dementia/neurocognitive issues due to HIV infection.

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comorbidity: co-occurrence of two disorders in the same individual

diagnosis: determination of which disorder a set of symptoms represents

Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5): authoritative index of mental disorders and the criteria for their diagnosis; published by the American Psychiatric Association (APA)

externalizing problems: problems related to disruptive behavior that cause conflicts in relationships with others

internalizing problems: problems that involve emotional alterations of anxiety disorders and depression

  1. Hannah Ritchie and Max Roser (2018) - "Mental Health". Published online at OurWorldInData.org. Retrieved from: 'https://ourworldindata.org/mental-health' [Online Resource]
  2. Salavera, Carlos, Usán, Pablo, & Teruel, Pilar. (2019). The relationship of internalizing problems with emotional intelligence and social skills in secondary education students: gender differences. Psicologia: Reflexão e Crítica, 32, 4. Epub February 18, 2019. https://dx.doi.org/10.1186/s41155-018-0115-y
  3. Regier, D. A., Kuhl, E. A., & Kupfer, D. J. (2013). The DSM-5: Classification and criteria changes. World psychiatry: official journal of the World Psychiatric Association (WPA), 12(2), 92–98. https://doi.org/10.1002/wps.20050