Journal of Consulting and Clinical Psychology 1998, Vol. 66, No. 2, 323-326 In the public domain Lower Precombat Intelligence Is a Risk Factor for Posttraumatic Stress Disorder Michael L. Macklin and Linda J. Metzger Veterans Affairs Medical Center, Manchester, New Hampshire and Harvard Medical School Brett T. Litz Boston Veterans Affairs Medical Center and Boston University Richard J. McNally Harvard University Natasha B. Lasko, Scott P. Orr, and Roger K. Pitman Veterans Affairs Medical Center, Manchester, New Hampshire and Harvard Medical School The authors examined the relation between intelligenee and posttraumatic stress disorder (PTSD) by studying the association among precombat intelligence, current intelligence, and self-reported PTSD symptoms. Military aptitude test results were obtained in 59 PTSD and 31 non-PTSD Vietnam combat veterans who had undergone a psychodiagnostic interview and current intelligence testing. People with lower precombat intelligence were more likely to develop PTSD symptoms as assessed by the Clinician-Administered PTSD Scale even after adjustment for extent of combat exposure. The association between current intelligence and PTSD was no longer significant after adjusting for precombat intelligence. These results suggest that lower pretrauma intelligence increases risk for developing PTSD symptoms, not that PTSD lowers performance on intelligence tests. Intensity of combat exposure is a critical factor in the develop- ment of posttraumatic stress disorder (PTSD) in Vietnam veter- ans. In the National Vietnam Veterans Readjustment Study (NVVRS; Kulka et al., 1990), extent of exposure to war-zone threats remained the best predictor of PTSD symptoms even after controlling for the effects of age, race, socioeconomic status (SES), and premilitary mental health. Most combat veterans do not develop PTSD (Kulka et al., 1990). Therefore, researchers have begun to study variables that may increase risk for the disorder among individuals exposed to combat. Lower cognitive ability may be one such variable. Lower levels of educational achievement were associated with more PTSD symptoms in the NVVRS (Kulka et al., 1990) and predicted PTSD in another study (Green, Grace, Lindy, Gleser, & Leonard, 1990). Pitman, Orr, Lowenhagen, Macklin, Michael L. Macklin, Linda I. Metzger, Natasha B. Lasko, Scott P. Orr, Roger K. Pitman, Psychiatry Service, Veterans Affairs Medical Center, Manchester, New Hampshire, and Department of Psychiatry, Harvard Medical School; Brett T. Litz, National Center for Posttraumatic Stress Disorder Behavioral Sciences Division, Boston Veterans Affairs Medical Center, and Department of Psychiatry, Boston University; Richard J. McNally, Department of Psychology, Harvard University This project was supported by Veterans Administration merit review grants and National Institute of Mental Health Grant MH51927. We thank Barbara Bauman, Joan Blume, Heike Croteau, Robert Ham- ilton, Susan Orsillo, and Elizabeth Roemer for technical assistance and Jordan B. Peterson for his comments on this research. Correspondence concerning this article should be addressed to Rich- ard J. McNally, Department of Psychology, Harvard University, 33 Kirk- land Street, Cambridge, Massachusetts 02138. Electronic mail may be sent to rjm@wjh.harvard.edu. and Altman (1991) found that a lower score on the Arithmetic Reasoning subtest of the Armed Forces Qualification Test (AFQT; Maier, 1993) at military enlistment (or induction) pre- dicted chronic PTSD following combat. The Centers for Disease Control Vietnam Experiences Study (1988) found that the lower a veteran's enlistment (or induction) General Technical score, which is the average of scores on the AFQT's Arithmetic Rea- soning and Verbal subtests, the greater the likelihood of his reporting poorer psychologic status after discharge from the military. The rate of PTSD was 65% among Operation Desert Storm (ODS) veterans who performed graves registration du- ties, and their mean intelligence was 91 (Sutker, Uddo, Brailey, Vasterling, & Errera, 1994). In a study of the relation between PTSD symptoms and cur- rent intelligence (McNally & Shin, 1995), regression analyses indicated that scores on the Combat Exposure Scale (CES; Keane et al., 1989) accounted for 17% of the variance in scores on the Mississippi Scale for Combat-Related PTSD (M-PTSD; Keane, Caddell, & Taylor, 1988). Full-scale intelligence, as esti- mated by scores on the Shipley Institute for Living Scale (Za- chary, 1991), accounted for an additional 10% of the variance in M-PTSD scores. Lower intelligence scores were associated with more severe PTSD symptoms. Although these findings suggest that lower intelligence may be a risk factor for combat- related PTSD, McNally and Shin cautioned that chronic PTSD symptoms (e.g., difficulty concentrating) may have impaired intelligence test performance in these individuals. Finally, study- ing ODS veterans, Vasterling, Brailey, Conslans, Borges, and Sutker (1997) reported a correlation between intelligence and PTSD symptoms (/• = —.37) nearly identical to that reported by McNally and Shin (r = -.33). Limitations in previous studies make it impossible to deter- 323