Epidemiology and Comorbidity
Phobias are among the most common psychiatric disorders. Findings based on large community samples from five sites in the Epidemiological Catchment Area (ECA) study (Eaton et al., 1991) yielded lifetime prevalence estimates of 11.25% for specific phobias and 2.73% for social phobia. Estimates from the National Comorbidity Survey (NCS) (Kessler et al., 1994) were consistent with previous findings on specific phobias: a lifetime prevalence of 11.30% in a sample of more than 8000 individuals from across the USA. The recent NCS-Replication study found lifetime prev-alence rates of 12.5% and 12.1 respectively for specific phobia and social phobia (Kessler et al., 2005).
Specific phobias are more common in women than in men, although there are differences in sex ratio among phobia types. Specifically, the ratio of females to males is smaller for height phobias than for other specific phobia types. Among social pho-bia situations, sex differences are less pronounced than for most specific phobia types. In the NCS, relatively small sex differ-ences in social phobia prevalence were confirmed, with lifetime estimates of 11.1% for males and 15.5% for females. In addition, the relatively equal numbers of men and women with social pho-bia in epidemiological studies is consistent with findings from samples of individuals presenting for treatment.
Most studies have found the mean age at onset of social phobia to be in the middle to late teens. This is supported by research finding that social phobia is common in children and is diagnosed in a significant percentage of children referred to a specialty anxiety disorders clinic. A history of childhood anxiety has been associated with an earlier age of onset of social phobia as well as greater severity and comorbidity. Mean age at onset for specific phobias appears to differ depending on the type of pho-bia. Phobias of animals, blood, storms and water tend to begin in early childhood, whereas phobias of heights tend to begin in the teens, and phobias of the situational type (e.g., claustrophobia) begin even later, with mean ages at onset in the late teens to mid-dle twenties.
The issue of comorbidity is important for several reasons. First, covariation among disorders provides valuable information about the nature of specific disorders as well as the utility of current di-agnostic nomenclature. For example, high rates of cooccurrence between two disorders could reflect overlap in the definitions of two disorders (as may be the case with social phobia and avoidant personality disorder) or shared etiological pathways. In addition, comorbidity may have implications for treatment. For example, an individual with social phobia who abuses alcohol might be less likely to benefit from treatment for social phobia if the alcohol abuse affects compliance with the social phobia treatment.
About 70% of individuals with blood phobias tend to have in-jection phobias as well. In addition, numerous factor analytical studies have found that blood-injection-injury phobias tend to cluster together as do animal phobias, natural environment pho-bias and situational phobias. In other words, having a phobia of one specific phobia type makes an individual more likely to have additional phobias of the same type than of other types. However, the clustering is not perfect and many studies show exceptions to this pattern. The research on the classification of specific pho-bia types is inconsistent. For example, in several of these stud-ies, height phobias tend to be associated with situational phobias (e.g., claustrophobia), despite height phobias being listed as an example of the natural environment type in DSM-IV.
Specific phobias tend to cooccur with other specific pho-bias. A recent methodologically rigorous study found that 15% of patients with a principal diagnosis of specific phobia also met criteria for another type of specific phobia and that 33% of pa-tients presenting with a principal diagnosis of specific phobia had additional symptoms that met criteria for an Axis I anxiety or mood disorder (Brown et al., 2001a). However, compared with individuals who have other anxiety disorders, individuals with principal diagnoses of a specific phobia are less likely to have additional diagnoses. Rather, specific phobias typically occur on their own or as additional diagnoses of lesser severity than the principal diagnosis. Studies confirm that specific phobias are a frequently occurring additional diagnosis, particularly with other anxiety disorders. However, specific phobias tend to occur less frequently in the context of other disorders such as depression (and alcohol use disorders.
Whereas the above mentioned studies reflect “syndrome” comorbidity, one can also discuss comorbidity at the “symptom” level. In other words, one can examine the frequency with which specific fears are associated with disorders regardless of whether they meet criteria for specific phobia. It appears that specific pho-bias commonly occur as additional diagnoses, at both clinical and subclinical levels.
Social anxiety is a feature of many disorders. Individuals with panic disorder, obsessive–compulsive disorder, or eating disor-ders often avoid social situations because of the possibility of being judged negatively if their symptoms are noticed by oth-ers. However, to meet diagnostic criteria for social phobia, one’s concerns must not be exclusively related to the symptoms of another disorder. With this criterion in mind, social phobia still tends to be associated with a variety of other DSM-IV disorders. Furthermore, unlike specific phobias, social phobia is frequently associated with additional disorders of lesser severity. One study conducted in two outpatient clinics in a managed care setting found a comorbidity rate of 43.6% in patients with generalized social phobia (Katzelnick et al., 2001). In another study, almost 60% of patients with social phobia had additional symptoms that met criteria for one or more additional diagnoses (Sanderson et al., 1990). The most frequently assigned additional diagnoses in this study were specific phobias (25%), dysthymia (21%) and panic disorder with agoraphobia (17%). The presence of comor-bid mood disorders has been associated with a greater duration of social phobia as well as more severe impairment before and after cognitive–behavioral therapy (CBT). Other studies have found that panic disorder with or without agoraphobia, generalized anxiety disorder, major depressive disorder and substance abuse are common additional diagnoses as well. In one prospective study, an estimated relative risk ratio of 2.30 for alcohol abuse or dependence was found in individuals with subclinical social phobia relative to individuals without social phobia or subclinical social fears, suggesting that individuals with subclinical social phobia were more than twice as likely to develop alcohol use dis-orders than were individuals without social phobia or subclinical social anxiety (Crum and Pratt, 2001).
As an additional diagnosis, social phobia is often assigned in patients with panic disorder with agoraphobia, generalized anxiety disorder, obsessive–compulsive disorder and major de-pressive disorder. Social phobia is also common among patients with eating disorders and alcohol abuse. When social phobia coexists with a mood disorder, substance abuse disorder, or another anxiety disorder, the social phobia tends to predate the other disorder. Treatment of these disorders should include com-ponents that address the social phobia when both disorders occur together.