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Psychological Effects - Nature vs. Human-caused Disasters

The Range, Magnitude, and Duration of Effects of 
Natural and Human-Caused Disasters: 
A Review of the Empirical Literature

October 4, 2001

The National Center For Post Traumatic Stress Disorder (PTSD)
<Read This Study On The NCPTSD>

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Posted On: January 20, 2002          Updated On: January 20, 2002
© Terence T. Gorski, 2001

The Range, Magnitude, and Duration of Effects of 
Natural and Human-Caused Disasters: 
A Review of the Empirical Literature

October 4, 2001

The National Center For Post Traumatic Stress Disorder (PTSD)
<Read This Study On The NCPTSD>

Prepared by: Fran H. Norris, Georgia State University, with the assistance of: Christopher M. Byrne and Eolia Diaz, Georgia State University, and Krzysztof Kaniasty, Indiana University of Pennsylvania

A total of 177 articles that described results for 130 distinct samples composed of over 50,000 individuals who experienced 80 different disasters were coded as to:

    disaster type (62% natural disasters, 29% technological disasters, and 9% mass violence)

    disaster location (60% USA, 25% other developed country, 15% developing country)

    sample type (73% adult survivors, 16% youth, 11% rescue/recovery workers)

    several methodological variables

After a preliminary review of the studies, each sample was coded as to the presence of 6 sets of outcomes and rated as to its overall severity of impairment.

Range of Outcomes

Specific psychological problems were identified in 74% of the samples. Posttraumatic stress or PTSD was found in 65% of the samples, depression or major depression disorder was found in 37% of the samples, and anxiety or generalized anxiety disorder was found in 19% of the samples. Panic disorder and specific phobias were rare.

Non-specific distress, assessed by means of global indices of psychological and psychosomatic symptoms, was identified in 39% of the samples.

Health problems and concerns, such as self-reported somatic complaints, verified medical conditions, increased taking of sick leave, elevations in physiological indicators of stress, declines in immune functioning, sleep disruption, increased use of substances, and (if previously disabled) relapse and illness burden, were identified in 25% of the samples.

Chronic problems in living, identified in 10% of the samples, were assessed rarely but generally found where they were assessed. Such problems included troubled interpersonal relationships, social disruption, family strains and conflicts, excess obligations to provide support, occupational stress, financial stress, environmental worry, and ecological stress.

Psychosocial resource losses were also assessed less frequently than the first 3 sets but nonetheless found in 10% of the samples. Declines in perceived support, social embeddedness, coping self-efficacy, and optimism were at least occasionally observed.

Problems specific to youth included various behavioral problems and separation anxiety among children, and deviance and delinquency among adolescent survivors.

Magnitude of Effects

To provide a rough estimate of the overall impact of the events studied, each sample's results were classified on a 4-point scale of severity:

    9% showed minimal impairment, meaning that the majority of the sample experienced only transient stress reactions;

    52% showed moderate impairment, wherein prolonged but subclinical distress was the predominant result;

    23% showed severe impairment, meaning that 25% to 49% of the sample suffered from criterion-level psychopathology; and

    16% showed very severe impairment, meaning that 50% or more of the sample suffered from criterion-level psychopathology.

Variables Which Predicted the Sample's Overall Severity of Impairment

School-aged youth were most likely, and rescue/recovery workers least likely, to show severe impairment: 62% of the school-aged samples experienced severe impairment, compared to 39% of the adult survivor samples and 7% of the rescue/recovery samples.

Developing countries were at greatest risk when location of the disaster was considered. Severe effects were observed in 27% of the U.S. samples, 46% of the samples from other developed countries, and 79% of the samples from developing countries.

Mass violence was, by far, the most disturbing type of disaster. Of the samples that experienced mass violence, 67% were severely impaired, compared to 34% of the samples who experienced technological disasters, and 42% of the samples who experienced natural disasters.

Disaster type and disaster location interacted to predict the sample's impairment. Almost all samples from developing countries experienced natural disasters, many of which were catastrophic in scope, involving high death tolls. Natural disasters in developing countries yielded a higher mean severity rating than did either natural or technological disasters elsewhere. However, within the developed countries, technological disasters had a significantly higher aggregate severity rating than did natural disasters. Thus, for the narrower purpose of understanding the typical impact of disasters in the United States, it is reasonable to expect that technological disasters, on average, will be more psychologically stressful than natural disasters. Technological disasters, however, were less disturbing than disasters of mass violence in both the United States and other developed countries.

Together, these 3 variables (disaster type, location, sample type) explained 30% of the variance in the sample's severity of impairment. The multiple correlation was .54.

Disasters in the United States

It was possible to identify several well-known events that were illustrative of disasters that had atypically weak, typical, or atypically strong effects on psychological outcomes.  Common denominators among events and samples are outlined below.

Atypically weak disasters were associated mostly with minimal impairment in the samples studied. These were exemplified by the 1989 Loma Prieta earthquake, the 1994 earthquake in Northridge, California, and the 1982 flood/dioxin contamination in the St. Louis Epidemiologic Catchment Area. Most samples in this group were not very seriously exposed or experienced little social disruption or had access to substantial personal and community resources.

Typical disasters were associated with moderate impairment in the samples studied. These were exemplified by the 1981 flood in Kentucky, Hurricane Hugo in 1989 in the Carolinas, and the 1979 nuclear accident at Three Mile Island. The diversity of events in this category point to a variety of processes that intersect to produce or protect against prolonged stress and distress. The effects of highly destructive events, such as Hugo, may be reduced by strong interpersonal and community supports, whereas the effects of less destructive events, such as the KY floods in Appalachia, may be heightened by a low-resource context. Even in the absence of trauma and actual property loss, the effects of technological accidents may be comparable in magnitude because of victims' residual uncertainties, health concerns, and loss of trust.

Atypically strong disasters were associated mostly with severe or very severe impairment. These were exemplified by Hurricane Andrew in 1992 in south Florida, the 1972 dam collapse in Buffalo Creek, West Virginia, the 1989 Exxon Valdez oil spill off the coast of Alaska, and the 1995 bombing of the Murrah Federal Building in Oklahoma City. These events caused massive destruction or threat to life and/or prolonged social and financial disruption and resource loss.

Duration of Effects

Twenty-seven panel studies (studies in which the same individuals are interviewed on multiple occasions) provided data on the course of postdisaster distress. Three primary trends were observed:

    First, the general rule, observed in the vast majority of studies, was for samples to improve as time passed. These effects were not always simply linear, as some outcomes sometimes improved for a while, then stabilized or worsened for awhile, then improved again.

    Second, levels of symptoms in the early phases of disaster recovery were good predictors of symptoms in later phases. Delayed onsets of psychological disorders were rare.

    Third, symptoms usually peaked in the first year and were less prevalent thereafter, leaving only a minority of communities and only a minority of individuals within those communities substantially impaired.

Summary and Conclusions

A substantial amount of research pertinent to understanding the range, magnitude, and duration of the effects of disasters has been published over the past 20 years. A variety of events were studied in a variety of ways, the samples were impressively diverse, and individuals' experiences ranged from little more than inconvenience to severe trauma and loss. Accordingly, it is not surprising that results varied, with some samples showing only minimal and transient stress reactions and others showing prevalent and persistent psychopathology. Several conclusions can be drawn on the basis of the literature reviewed for PART I:

The range and distribution of outcomes suggests that a quality assessment of victims' mental health should include, at minimum:

    a retrospective diagnostic assessment of PTSD, preferably one that anchors the symptoms to the disaster

    a brief measure of current nonspecific distress

    an inventory of the acute and chronic stressors and resources losses associated with the event.

Allowing 20 questions for (1), 10 questions for (2), and 20 questions for (3), a 50-item screening tool could be developed for use in the field. Such a measure could be completed by most adults in 20 minutes or less.

The relative risk of sample types, in which youth were at greatest risk and rescue/recovery workers the least, points to an advantage of maturity and experience.  In light of recent events in the United States, the effect for recovery workers should be interpreted with caution. While often exposed to horror, these rescue and recovery workers seldom experienced direct losses or extensive bereavement. However, it is also possible that we could learn from the capacity of such workers to support one another and to develop a meaningful narrative about their experience.

That samples from outside the United States tend to be more severely impaired likely reflects the fact that disasters tend to be more destructive when they occur in the developing world. Many of the samples from developing countries survived disasters where death tolls were measured in thousands or even tens of thousands. If this effect reflects the importance of surviving in a context of massive destruction and death, rather than location per se, it may have relevance for the United States as it now grapples with the aftermath of a disaster of comparable enormity. The difference may also attest to the ability of government services and other resources to make a difference in the lives of disaster victims.

Findings regarding the adverse consequences of experiencing disasters caused by malicious human intent were unequivocal. In the United States, technological disasters appear to be somewhat more stressful than natural disasters. From a more global perspective, it may be time to re-examine our ideas about the relative impact of natural and technological events. The literature in the field has changed markedly in the past decade. International research has mushroomed and many of these studies have found quite severe effects. Many of our ideas about the course of recovery from natural disasters are based very much on western experience where predisaster housing quality, controls over land use, and warning systems are far superior to the norms in developing countries.

It should also be recognized that both natural and technological disasters varied considerably in their effects, as we found examples of low impact, moderate impact, and high impact events within each of these categories. Few of the incidents of mass violence had anything other than severe effects.

Overall, from these illustrative studies and others similar to them in the database, we may conclude that disasters should have minimal consequences for mental health at the population level beyond those associated with transient stress reactions when:

    injuries and deaths are rare

    the destruction or loss of property is confined relative to the size and resources of the surrounding community

    social support systems remain intact and function well

    the event does not take on more symbolic meanings of human neglect or maliciousness

Such events may compose a minority of those in the published literature, but probably a larger share of real life events in the United States. Such events probably do not require large-scale professional or even paraprofessional mental health interventions, although crisis intervention strategies that ameliorate the initial stress may be helpful.

At a moderate level of impact, the typical result for major disasters in the United States, programs that can reduce stress, enhance social support, and provide reassurance about future risk are advisable at the community level. Such programs might encompass mechanisms for identifying and referring the minority of those with more serious impairment for professional treatment.

Disasters that engender severe, lasting, and pervasive psychological effects are rare, but they do happen. Sample (and presumably population) level affects were greatest when at least 2 of the following event-level factors were present:

    Extreme and widespread damage to property.

    Serious and ongoing financial problems for the community

    Human carelessness or, especially, human intent caused the disaster.

    High prevalence of trauma in the form of injuries, threat to life, and loss of life.

When such disasters occur, the need for professional mental health services will be widespread. Delivering them will pose a tremendous challenge but seems to be required.

Persons who are most at risk for long-term distress can be identified fairly early in the process, which therefore points to a need for early screenings and interventions in disaster mental health.


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