Anxiety and depression disorders are difficult to differentiate because they often have overlapping symptoms. It is estimated that approximately 20 percent of patients have such mixed symptoms that they cannot be definitely categorized as suffering from either anxiety or from depression (Cloninger, 1989). Another 20 percent have symptoms of both disorders, and approximately two-thirds of patients who are diagnosed as suffering from major depression also have symptoms of anxiety (Fawcett and Kravitz, 1983). There are also many other factors involved in making the diagnosis which may make an absolute diagnosis of anxiety or depression difficult (Cloninger, 1990). These include the fact that both disorders may have common genetic/familial features, i.e. a family history of the disorder; both disorders have similar comorbid profiles; both disorders are often brought on by similar stressful life events; often both disorders are assessed using the same psychological tests; and often the same drugs, such as the tricyclic antidepressants, are used for treatment of both of the disorders (Gersh and Fowles, 1979).
Making the matter even more confusing is the fact that it has also been suggested by different research groups that a combination of symptoms of both depression and anxiety may represent a separate disorder in itself (Gersh and Fowles, 1979); that anxiety and depression are two distinct disorders (Mountjoy and Roth, 1982); and that anxiety and depression form a mixed syndrome (Paykel, et al, 1982). Patients exhibiting both depression and anxiety seem to have a poorer prognosis than those exhibiting just one symptom (Shapira et al, 1972), and may also exhibit an increased risk of suicide in these patients (Fawcett et al, 1990). This would suggest that comorbid or mixed states of depression and anxiety may represent a more serious psychological disorder than just depression or anxiety alone (Van Valkenberg et al, 1984).
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