Different factors are associated with an increased risk of developing post-traumatic stress disorder following a traumatic event: being a woman, having been exposed to several previous traumatic events, dissociating during or after the traumatic event, coping with many other life stressors, using passive stress management strategies (i.e., coping), low self-efficacy, physical injuries during the traumatic event, the severity of the event and its interpersonal nature, dealing with previous mental health problems and having precarious or negative social support. Conversely, some factors are associated with a decreased chance of developing post-traumatic stress disorder. These protective factors include having rich and positive social support before and after the event, receiving effective social support during or shortly after the event, using active stress management strategies and having a strong sense of personal effectiveness. Although significant, the size of the effect of these factors remains modest. Overall, the factor operating before, during and after the trauma most strongly associated with PTSD is social support; the absence of which is positively associated with PTSD, while its presence is negatively associated.