The scale is scored as the mean of item scores. The IES-R yields 3 subscales (avoidance, intrusion, and hyperarousal) and a total score. The three

subscales have strong internal consistency and satisfactory test-retest reliability [17]. The correlation between the Mississippi Scale for Combat-Related PTSD, Civilian Version and the three subscales of the IES-R were: Intrusion, r=.53, Avoidance, r=.55, and Hyperarousal, r=.55 [18]. Cronbach’s alpha for the total scale was 0.91. In the current sample 56 participants (25%) identified the index IES-R event as the critical incident, 126 (55%) indicated some other experience and 46 (20%) did not specify an event. Inhibitors,research,lifescience,medical IES-R scores were non-parametrically Inhibitors,research,lifescience,medical distributed and skewed toward the minimum score (median 0.7, inter-quartile range 0.3 – 1.0). Burnout The 9-item emotional exhaustion subscale of the Maslach Burnout Inventory Human Services Survey shows strong reliability and validity [19]. Responses describe the frequency of phenomena over a long period (up to a year) on a seven-point scale from 1 (never) to 7 (every day). Burnout scores were approximately normally distributed (mean 21.8±11.6) and Cronbach’s alpha was 0.92. Data analysis Strategy to develop and validate the inventory There is no gold standard method of indentifying the characteristics of a critical incident that are likely to cause emotional sequelae. Our strategy Inhibitors,research,lifescience,medical was to assemble an inclusive inventory of potential

characteristics and then to reduce Inhibitors,research,lifescience,medical the number of items by retaining only those whose relationship with peritraumatic distress was above a threshold. Retained items were then sorted into logical categories. We categorized characteristics of events that might present such an overwhelming threat into three types:

situational, systemic and personal. Factor analysis was not appropriate because the instrument is an inventory of heterogeneous characteristics, not a scale. For example, there is no a priori reason to expect that an event involving one this website situational characteristic (e.g. a child was involved) would be more likely than any other event to also involve another situational characteristic (e.g. the situation Inhibitors,research,lifescience,medical was dangerous for me). For these the same reason, the quantitative outcome of the inventory was not a score but a tally and measures of internal reliability were not appropriate. Two types of indices were derived: endorsement of any characteristic in a domain, and the total number of characteristics endorsed. We then calculated the relationship between indices derived from the inventory and measures of the phenomena which are expected a priori to result from the distress caused by critical incidents: peritraumatic dissociation, the occurrence and delayed recovery from the Acute Stress Reaction and psychological symptoms occurring long after the event. Development of the inventory based on relationship of items to peritraumatic distress 1. Selection and classification of inventory items.