It is difficult to estimate how many veterans in the United States suffer from PTSD, but estimates range from 500,000 to 1.5 million (Kulka et al., 1990). The large numbers of veterans affected and a greater appreciation for the disabling effects of PTSD have inspired an increased research effort on the causes, psychological and physiological mechanisms, diagnostic criteria, course, and treatment of PTSD. Although it is impossible to review all of this work here, examples of this research bear directly on some of the key aspects of the experiences of veterans who contacted this committee.
A recent study of Vietnam veterans examined the kind of stressors most likely to result in PTSD in combination with other psychological disorders, including depression, panic disorder, phobic disorder, and alcoholism (Green et al., 1989). Over 52 percent of the sample of 196 individuals met the criteria for some type of psychiatric disorder: 29 percent met the criteria for PTSD, 21 percent were found to have phobic disorder, 15 percent suffered from major depression, 11 percent were alcoholic, and 7 percent exhibited panic disorder. Interestingly, a little more than 10 percent met criteria for both PTSD and major depression, and over 14 percent had both PTSD and phobic disorder. When these disorders were correlated with specific types of military experiences, some intriguing associations emerged. For example, the younger the individuals were entering the military, the higher was the percentage of PTSD found. In addition, the most potent predictor of PTSD and anxiety disorder comorbidity (PTSD with phobic or panic disorder) was involvement in dangerous and high-pressure "special assignments." Exposure to grotesque scenes of death and mutilation was associated with higher incidence of multiple disorders (e.g., PTSD and some other disorder, but no one disorder in particular). None of the results could be reliably attributed to psychiatric conditions prior to the war experiences.
Reasonable arguments may be made that Vietnam veterans, as a group, are quite different from WWII veterans due to a difference in the public perception of the respective conflicts, generational value differences, and other variables. Davidson and colleagues (1990) have compared Vietnam veterans with WWII and Korean War veterans on measures of depression, anxiety, severity and types of symptoms, and intensity and nature of combat experiences. The two groups of veterans were generally the same in terms of the sequential emergence of diagnoses and the age of onset of diagnoses: PTSD was followed by a general anxiety, which was then followed by panic disorder, major depression, and intermittent depressions. Alcoholism tended to emerge later in World War II and Korean War veterans than in Vietnam veterans. In addition, Vietnam veterans had, among other