Commentary

At first glance, this important, clearly written, and self critical review by Brewin et al shows that many risk factors contribute to PTSD. This, however, is mostly due to the large number of participants included in each analysis. When effect sizes are considered, a different story emerges, mainly showing that the intensity of the traumatic event and factors that follow exposure (“social support” and “further stressors”) are the strongest predictors of PTSD, whereas “previous” (ie, pre-traumatic) factors have smaller individual effects (combined effects were not computed). Thus, once a traumatic event has occurred, the major risk factors for PTSD appear to lie ahead, suggesting ample opportunity for secondary prevention of this disorder. Such a conclusion, however, might have to be reserved for several reasons. Firstly, the proximity of later predictors to the time at which questions were asked could have aggrandised their reported effect. Secondly, this meta-analysis did not address interaction between risk factors. Thirdly, pre-trauma risk factors could affect the survivors' responses to and perception of the traumatic event, and their capacity to respond to rewarding social interaction during the period of recovery. Fourthly, pre-trauma and post-trauma risk factors may have a common source (eg, living environment in which life stressors abound).

Importantly, this work puts the simple causal link between traumatic events and subsequent PTSD into proportion. Trauma exposure is, indeed, a trigger. Preceded by as many vulnerability factors as this work depicts, and followed by potent reinforcing or maintaining factors, the impact of the traumatic event is determined by a chain reaction. Surprisingly, this work did not capture major differences between methods of enquiry (eg, prospective or retrospective; questionnaires or interviews) and populations studied. The differences that were captured wisely show that generalisations are risky and that the relative weight of risk factors should be reconsidered in each case. The role of biological risk factors was not addressed, yet pertinent evidence may become available in the future.