Identifying the nature of the event that allegedly caused the injury also needs to recognize recent research developments. Whereas DSM-III-R described the stressor as 'a psychologically distressing event that is outside the range of usual human experience' (APA, 1987), DSM-IV (APA, 1994) deleted this constraint. These changes have allowed a wider range of events to be claimed as possible causes of the disorder. Prior to the definition of PTSD in DSM-IV, there was much concern from legal representatives that broadening the definition to the point of not specifically defining the stressor would create excessive opportunity for people to claim damages based on a PTSD presentation. Most jurisdictions adhere to the principle of foreseeability, in which one would expect the injury to occur following the relevant event (Spaulding, 1988). There is much research that informs us about the likelihood of PTSD developing after a specific event. There is largely a direct relationship between the severity of the stressor and the likelihood of PTSD developing (March, 1993). Although there are reports of PTSD occurring after less threatening events (e.g. Burstein, 1985), claims of PTSD developing following minor incidents that do not typically lead to PTSD should be questioned because they are inconsistent with the scientific knowledge of the precipitants of PTSD.
Recent research in the field of PTSD has also indicated the importance of obtaining independent verification of the claimant's accounts of the event. Police, insurance, medical, or military records may be available to verify the reported details about the event, and the claimant's reaction to the event. People's recall of traumatic events can change over time (Wagenaar and Groeneweg, 1990). More importantly, how the event is recalled can be influenced by their current psychological state (Southwick et al., 1997). Prospective studies have reported that people's recall ofpsychological states, including pain (Bryant, 1993) and PTSD symptoms (Harvey and Bryant, 2000), is influenced by their mood at the time of recall. In a recent study of motor vehicle accident survivors who lost consciousness in the accident as a result of brain injury, 40% reported two years after the accident that they had fully recovered their memories of the incident (Harvey and Bryant, 2001). This pattern highlights the possibility that retrospective reports of a traumatic incident can be reconstructed in ways that are not consistent with historical accuracy. Documentation that can independently verify the nature of the event, and the claimant's response, allows the psychologist to make stronger inferences about the relationship between the event and the reported psychological injury.
In determining causation, courts typically focus on the constructs of proximity, remoteness, and foreseeability (Douglas et al., 1999). These constructs typically result in courts deciding causation in terms of the injury being proximally related to the event. If it cannot be established that the psychological injury commenced in proximity to the alleged causal event, then serious doubts are held about the role of the alleged event. In the case of PTSD, DSM-IV permits 'delayed onset PTSD' to be diagnosed when the symptoms commence more than six months after the event. There are case studies of delayed onset PTSD commencing 30 years after the precipitating event (van Dyke, Zilberg and McKinnon, 1985). This possibility raises marked problems for the psychological assessment because one needs to determine the causal link between currently reported symptoms and an event that may have occurred many years earlier. Negligence laws in both Canada (Athey v. Leonati, 1996, SCC) and the USA (Chaney v. Smithkline Beckman Corp., 1985; US 8th Circuit Ct) have rested on the 'but for' test. This test requires that for causation to be determined, it must be proved that an injury would not have occurred had it not been for a negligent act. Determining this issue can be complex. For example, in 1964 Australia suffered its worse naval disaster when an aircraft carrier collided with a destroyer that subsequently sunk and 81 sailors drowned. More than 35 years later there have been hundreds of claims for PTSD by personnel who were on the aircraft carrier at the time, and a significant proportion of these have involved delayed onset PTSD. Delineating the influence of the collision on a sailor's psychological state is difficult when the psychologist needs to determine the individual's functioning immediately after the collision, during the many years following the event, and identifying other stressors that may have been associated with the delayed onset of the reported PTSD symptoms. This scenario highlights the importance of integrating research findings into the psychological assessment because, whereas there are many case reports of delayed onset PTSD, properly conducted prospective studies suggest that so-called delayed onset PTSD probably reflects people who have been symptomatic since the time of the trauma but have not met full diagnostic criteria until more recent times (Bryant and Harvey, in press-b; Buckley, Blanchard and Hickling, 1996; Ehlers, Mayou and Bryant, 1998). The psychologist needs to interpret claims of delayed onset PTSD in relation to the scientific data that describe the current knowledge about the relationship between the event and the onset of psychological injury.
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