Journal of Consulting and Clinical Psychology

Meta-analyses were conducted on 14 separate risk factors for posttraumatic stress disorder (PTSD), and the moderating effects of various sample and study characteristics, including civilian/military status, were examined. Three categories of risk factor emerged: Factors such as gender, age at trauma, and race that predicted PTSD in some populations but not in others; factors such as education, previous trauma, and general childhood adversity that predicted PTSD more consistently but to a varying extent according to the populations studied and the methods used; and factors such as psychiatric history, reported childhood abuse, and family psychiatric history that had more uniform predictive effects. Individually, the effect size of all the risk factors was modest, but factors operating during or after the trauma, such as trauma severity, lack of social support, and additional life stress, had somewhat stronger effects than pretrauma factors. ---------------------------------------------Originally, posttraumatic stress disorder (PTSD) was conceptualized as a normal response to overwhelming psychic trauma. Partly on the basis of accumulating evidence for wide variation in the prevalence of PTSD following exposure to different kinds of stressor, there is increasing acceptance of the idea that exposure to a trauma may not always be sufficient to explain the development of PTSD and that individual vulnerability factors have a role to play in understanding this condition (e.g., Yehuda, 1999; Yehuda &#38; McFarlane, 1995). The impact on later PTSD of trauma intensity, pretrauma risk factors, and other aspects of vulnerability has been reviewed by, among others, Shalev (1996). Shalev summarized the results of 38 studies and identified numerous risk factors for PTSD, including pretrauma vulnerability (e.g., family history of mental disorders, gender, genetic and neuroendocrine factors, personality traits, early traumatization, negative parenting experiences, and lower education), the magnitude of the stressor, preparation for the event, immediate reactions to the trauma (e.g., dissociation and coping responses), and posttrauma factors (e.g., emerging symptoms, social support, and other life stress). Much of the evidence that has formed the basis of previous reviews has derived from studies of combat veterans and may not be generalizable to civilian samples. Moreover, the studies are extremely heterogeneous (see discussion below) and results for individual risk factors have not always been consistent (e.g., Bremner, Southwick, &#38; Charney, 1995). In this situation, with a relatively large number of relevant studies varying simultaneously along several dimensions, an accurate summary may best be given using meta-analytic techniques. Previous meta-analyses in the trauma field have examined the general psychological impact of military service in Vietnam (Kaylor, King, &#38; King, 1987), disasters (Rubonis &#38; Bickman, 1991), or interpersonal violence (Weaver &#38; Clum, 1995). Neither risk factors nor the specific diagnosis of PTSD have yet been studied in this way. Given the current debate concerning the relative importance of the trauma itself versus other vulnerability factors in the development of PTSD, and the need to build comprehensive models of PTSD that take into account the rapidly growing numbers of empirical studies, it would be valuable to have more broadly based quantitative estimates of the absolute and relative effect sizes associated with the various possible risk factors. In this article, we present a series of meta-analyses of currently available studies yielding effect sizes for a variety of risk factors for PTSD and examine whether these effect sizes are homogeneous or whether they are affected by characteristics of the study or the sample. In attempting to summarize the literature on risk factors for PTSD, several sources of variability should be acknowledged at the outset. These can be considered under the headings of design, sampling, and measurement. First, there have been relatively few prospective studies of PTSD that have measured risk factors before the traumatic event (one exception is Macklin et al., 1998), although others have measured risk factors posttrauma but prior to the onset of PTSD (e.g., Andrews, Brewin, Rose, &#38; Kirk, 2000). Much research has attempted to infer what were risk factors by comparing a group of people who have already contracted PTSD with a control group (e.g., Kelly et al., 1998). This raises the issue of whether the presence of PTSD biases estimates of premorbid personality and intelligence or affects retrospective reports of childhood history or trauma severity. Although there is reassuring evidence that some types of psychopathology (such as depression) do not typically bias reports of childhood experience (Brewin, Andrews, &#38; Gotlib, 1993), little is known about the possible impact of PTSD on such reports. It will be important to investigate, where possible, whether prospective and retrospective designs yield similar estimates of effect size. Studies vary on several dimensions other than the longitudinal-retrospective one. The modal strategy adopted by investigators has been to examine the relation of risk factors to PTSD in a population of people all exposed to trauma. However, some studies have reported risk factors for PTSD in trauma survivors based on comparisons with controls who may not have been exposed to trauma, an approach that seeks to predict the joint risk of trauma exposure and the development of subsequent PTSD (e.g., Wolfe et al., 1998). Other studies have compared risk factors for PTSD versus other clinical conditions in a trauma-exposed sample, thereby attempting to predict what is unique about posttraumatic versus other symptoms of psychopathology (e.g., Watson, Davenport, Anderson, Mendez, &#38; Gearhart, 1998). Still other studies have reported predictors of symptom severity within a sample who all have either PTSD or some other psychiatric disorder, thereby focusing on gradations of disorder within a clinical population (e.g., McFall, Mackay, &#38; Donovan, 1991). Thus, investigators have addressed a number of equally valid but quite separate questions, and it cannot be assumed that the risk factors identified will be consistent across these different designs. In practice, there are only enough studies using the first, modal strategy to justify a meta-analysis. The samples in which PTSD has been studied are varied, including the general population, combat veterans, assault and rape victims, victims of motor vehicle and other types of accidents, victims of natural disasters, and people suffering from life-threatening medical conditions. By far the largest group studied is male combat veterans; in contrast, civilian studies have frequently focused on female trauma victims or have used samples in which both genders were well represented (e.g., Nishith, Mechanic, &#38; Resick, 2000; Ursano et al., 1999). It is important to investigate whether risk factors discovered in combat veteran studies, or in male samples, generalize to civilian and female samples. Apart from demographic factors that are routinely measured, there has been little consistency in the risk factors investigated in the different studies or in the measures used to assess them. Measures of trauma severity are reasonably consistent in studies of combat veterans, which have increasingly tended to focus on specific factors, such as high levels of perceived threat, exposure to atrocities or episodes of extraordinarily abusive violence, and on a general milieu of a harsh or malevolent environment (e.g., King, King, Gudanowski, &#38; Vreven, 1995). In contrast, measures of trauma severity in the civilian studies vary widely, both between different types of trauma and also within trauma types. This necessary heterogeneity is likely to decrease the reliability of effect size estimates, although the finding of consistent associations across different trauma types would tend to increase confidence in their validity. Another source of variability is the measure of PTSD used in the different studies. This typically consists of a dichotomous variable reflecting whether or not the person meets formal diagnostic criteria for the disorder laid down in the American Psychiatric Association&#39;s Diagnostic and Statistical Manual of Mental Disorders (3rd ed. [DSM&#150;III; American Psychiatric Association, 1980]; 3rd ed., rev. [DSM&#150;III&#150;R; American Psychiatric Association, 1987]; 4th ed. [DSM-IV; American Psychiatric Association, 1994]). Although remaining largely consistent, the diagnosis has changed somewhat in emphasis with succeeding versions of the DSM, particularly with the importance given to the impairment criterion in the DSM&#150;IV. It is possible that these changes will impact on risk factor estimates, although too few studies have used DSM-IV criteria to test this empirically. Occasionally, some investigators (e.g., Solkoff, Gray, &#38; Keill, 1986) have included together in their analyses participants meeting full diagnostic criteria for PTSD with those suffering from &#147;partial&#148; PTSD, and again there is no guarantee at present that the risk factors for the two conditions are the same. Diagnoses may also be current or lifetime. It is conceivable that studies requiring a current diagnosis will contain a higher proportion of chronic cases and that risk factors for chronic PTSD are somewhat different to those for brief episodes of the disorder. A comparison of effect sizes for studies using current and lifetime diagnoses would be helpful in this regard. However, in practice there are two limitations to this strategy. First, studies of current or lifetime PTSD only rarely report the length of time symptoms have been present. Second, many of the most important studies assessing lifetime PTSD in adults have used large epidemiological samples, have assessed a variety