Copyright 1992 by the American Psychological Association. Inc. 0022-006X/92/S3.00

Journal of Consulting and Clinical Psychoiogy 1992, Vol. 60, No. 3, 409-418

SPECIAL POPULATIONS: TRAUMA Epidemiology of Trauma: Frequency and Impact of Different Potentially Traumatic Events on Different Demographic Groups Fran H. Norris This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

Georgia State University The frequency and impact of 10 potentially traumatic events were examined in a sample of 1,000 adults. Drawn from four southeastern cities, the sample was half Black, half White, half male, half female, and evenly divided among younger, middle-aged, and older adults. Over their lifetimes, 69% of the sample experienced at least one of the events, as did 21% in the past year alone. The 10 events varied in importance, with tragic death occurring most often, sexual assault yielding the highest rate of posttraumatic stress disorder (PTSD), and motor vehicle crash presenting the most adverse combination of frequency and impact. Numerous differences were observed in the epidemiology of these events across demographic groups. Lifetime exposure was higher among Whites and men than among Blacks and women; past-year exposure was highest among younger adults. When impact was analyzed as a continuous variable (perceived stress), Black men appeared to be most vulnerable to the effects of events, but young people showed the highest rates of PTSD.

Over the past two decades, the study of life events has intrigued countless medical, behavioral, and social scientists. For the most part, this research has focused on events that are within the realm of normal human experience, such as changes in residence, jobs, or personal relationships. Although such changes are clearly important to the individuals who experience them, policies and programs at the community level are often more oriented toward responding to nonnormative events, such as criminal victimization, and collective crises, such as natural disaster. From a policy or population perspective, such assaults to public safety are all too familiar and common. For the individual, however, they are potentially quite traumatic. Exactly what constitutes a traumatic event is subject to debate. The American Psychiatric Association (1987) defines a traumatic event as one "that is outside the range of usual human experience and that would be markedly distressing to almost anyone" (p. 250). In their scheme, certain experiences qualify a priori as traumatic (e.g., threat to life, destruction of home) whereas others (e.g., divorce, illness) do not. Alternatively, some

This research was supported by Grant MH45069 from the Violence and Traumatic Stress Research Branch of the National Institute of Mental Health. Appreciation is extended to Betty A. Hanacek for her assistance with the research, to Bonnie L. Green and Krzysztof Kaniasty for their comments on a draft of this article, and to Southern Research Services (Louisville, Kentucky) for coordinating data collection. Correspondence concerning this article should be addressed to Fran H. Norris, Department of Psychology, GeorgiaState University, University Plaza, Atlanta, Georgia 30303.

409

investigators (Breslau & Davis, 1987; Solomon & Canino, 1990) have argued that what is important is whether the event is shocking to the individual, regardless of its form. According to these latter investigators, a traumatic event should be denned as any event that produces symptoms of traumatic stress (intrusion, numbing, and arousal). For research purposes, Norris (1990) proposed a more restrictive definition of traumatic events as the population of events involving "violent encounters with nature, technology, or humankind." She further defined a violent event as one that is marked by sudden or extreme force and involves an external agent. Interpersonal violence may be the obvious example, but the definition easily encompasses other threats to public safety such as fire, disaster, evacuation, and vehicular accidents. From this perspective, traumatic events are a subset of the larger population of life events, grouped together because they share common properties. Traumatic events are thus defined objectively, leaving their consequences for subjective states of stress as an empirical question. Of course, it is reasonable to assume that any event in this set is capable of eliciting extreme fear or aversion. For no class of life events do individual and public interests converge more readily. Individual citizens do what they can to avoid traumatic events but ultimately hold public officials responsible for their prevention and amelioration. Thus, in terms of the potential utilization of findings, traumatic stress is a particularly exciting area for research. Unfortunately, traumatic events are often difficult to study. Historically, traumatic stress studies have relied on small homogeneous samples or have focused on one particular event (e.g., rape) at a time. These methods have generally precluded our gaining a very in-depth un-

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410

FRAN H. NORRIS

derstanding of the relative frequency and severity of various traumatic events as they occur naturally in community populations. In recognition of this limitation in the earlier literature, attention to the epidemiology of trauma has increased in recent years. By and large, these studies have focused on estimating the prevalence of posttraumatic stress disorder (PTSD) following specific experiences such as disaster (4.6%; Robins et al., 1986) or Vietnam era combat (15%; Kulka et al, 1990). Helzer, Robins, and McEvoy (1987) appear to have been the first investigators to attempt to estimate the total prevalence of PTSD in the general population. On the basis of data provided by the Diagnostic Interview Schedule (DIS; Robins, Helzer, Croughan, Williams, & Spitzer, 1981) and the Epidemiologic Catchment Area Survey (EGA, St. Louis site), it appeared that only about 1 % of the total population met all criteria for lifetime PTSD ("lifetime" being the proportion of the population ever meeting diagnostic criteria). The Piedmont EGA yielded similar statistics (Davidson, Hughes, Blazer, & George, 1991). Following the EGA survey, the DIS was criticized for its lack of sensitivity to traumatic stress (e.g., Kulka et al., 1990; Solomon & Canino, 1990) and revised. Using this revised version on a sample of 1,000 adults aged 21-30, Breslau, Davis, Andreski, and Peterson (1991) conducted a landmark study in this area. Their estimates of the total frequency of traumatic events (39%), lifetime prevalence of PTSD within the exposed population (24%), and lifetime prevalence of PTSD within the general population (9%) far exceeded previous ones. They also provided an estimate for chronic PTSD (which requires symptoms to endure for at least 3 years). At 3.4%, this was roughly a third of the total lifetime rate. Still another recent and important epidemiological study has been conducted by Kilpatrick and Resnick (1992). They used a more detailed event inventory than provided by the DIS (either original or revised) to collect data from a national probability sample of 1,500 women. Unlike previous studies, they documented the current prevalence of PTSD (proportions meeting criteria now) as well as the lifetime prevalence of PTSD for various subsamples exposed to potentially traumatic events. Whereas lifetime rates of PTSD ranged from 10 to 39%, current rates ranged from 1 to 13%. Both rates were highest among women who had been raped or assaulted. My purpose likewise was to examine the frequency and impact of various traumatic events in a normal community-dwelling sample. Toward this goal, both past-year and lifetime frequency data for 10 different traumatic events were collected. Because of numerous methodological differences, the data are not directly comparable to those reported by Breslau et al. (1991). First, as in Kilpatrick and Resnick's (1992) study, multiple, specific screening questions were used to provide a more sensitive measure of traumatic events than the open-ended prompt used in the DIS. Second, the event data were interpreted only in light of current symptoms; no attempt was made to ascertain lifetime rates of disorder. A strength of the present study is the diversity of its sample, drawn from 12 neighborhoods across four mid-sized southeastern cities. The sample is racially heterogeneous (half White, half Black), a characteristic that is particularly important given the paucity of trauma research on civilian African Americans

(Neal & Turner, 1991). Moreover, the sample was drawn so that it is half male and half female and evenly divided among younger, middle-aged, and older adults. Therefore, it was possible to examine whether different subgroups of the population are differentially exposed or vulnerable to traumatic life events. If epidemiological data on traumatic life events are generally scarce, they are particularly so for certain segments of the population such as Blacks and older people. Method

Sample A sample of 250 persons was drawn from each of four cities: Charleston, South Carolina; Greenville, South Carolina; Charlotte, North Carolina; and Savannah, Georgia (N = 1,000). Hour-long interviews were conducted in the respondents' homes in October and November 1990. The primary purpose of the project was to study the long-term consequences of Hurricane Hugo, a natural disaster that had devastated large areas of North and South Carolina on September 22,1989. The sampling procedures reflect that goal. In the first phase of the sampling procedures, the investigators toured the peninsula (urban area) of Charleston and selected three census tracts. Criteria for selecting the tracts were that hurricane damage should still be evident (6 weeks after Hugo) and that different racial and economic groups should be represented. The investigators then toured the remaining three cities and selected neighborhoods of similar demographic and economic character as the Charleston tracts, including one area of public housing in each city. In Charlotte, the other city that was actually stricken by Hugo, neighborhoods also were selected on the basis of damages sustained in the disaster. Interviewers proceeded in specified order through the selected neighborhoods. Limits were placed on the number of interviews that could be obtained in any one block. For comparison purposes and to keep the samples from each city as similar as possible, a quota sampling strategy was used. This strategy provided approximately equal numbers of Blacks and Whites, men and women, and younger (18-39), middle-aged (40-59), and older persons (60+). Within certain limits of tolerance, the quota was fully balanced. A total of 404 persons refused to participate in the study, yielding a response rate of 71%. A sizable percentage (13%) refused for reasons related to health or distress, but the most common reason for refusal was simply lack of interest (83%). When a person selected for a quota sample refuses, he or she is replaced with someone else of the same cell (in this case, this was someone of the same neighborhood, race, sex, and age). This procedure does not preclude the occurrence of selection effects but should limit them. Differences between respondents and refusers were tested using an 8-item index of housing quality (a = .95). This scale was completed by the interviewer on the basis of external features of the dwelling (e.g., appearance of roof) and thus was independent of selected individuals' willingness to cooperate. In an analysis of variance, refusers (coded 0) did not differ from respondents (coded 1) on this measure, F(l, 1389) < 1. The comparability between refusers and respondents held for all subsamples, as indicated by tests of interactions between response and the variables of sex, F(l, 1382) < 1; race, F(l, 1377) < 1; age, F(2,1376) < 1; and city, F(3, 1382) = 1.57. Thus, the sample and subsamples are generally representative of the persons who were contacted concerning study participation.

Measures Traumatic life events. The Traumatic Stress Schedule (TSS; Norris, 1990) was used to collect lifetime and past-year incidence data on nine

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EPIDEMIOLOGY OF TRAUMA different traumatic events: robbery ("Did anyone ever take something from you by force or threat offeree, such as in a robbery, mugging, or holdup?"); physical assault ("Did anyone every beat you up or attack you?"); sexual assault ("Did anyone ever make you have sex by using force or threatening to harm you? This includes any type of unwanted sexual activity."); tragic death ("Did a close friend or family member ever die because of an accident, homicide, or suicide?"); motor vehicle crash ("Were you ever in a motor vehicle accident serious enough to cause injury to one or more passengers?"); combat ("Did you ever serve in combat?"); fire ("Did you ever suffer injury or property damage because of fire?"); other disaster ("Other than from Hurricane Hugo, did you ever suffer injury or property damage because of severe weather or either a natural or manmade disaster?"); and other hazard ("Other than from Hurricane Hugo, were you ever forced to evacuate from your home or did you otherwise learn of an imminent hazard or danger in your environment?"). In addition, the interview provided considerable data on injury, losses, and evacuations that were related to Hurricane Hugo. For the present study, however, these data were coded simply as (1) exposed (evacuated, personal loss, or both) or (0) unexposed. Perceived stress. Two continuous measures of perceived stress were used. Both were scored as the sum of values for scale items that all had the same 5-point response format (from never to very often). High scores indicate high perceived stress. The scales occurred early in the interview schedule, well before the questions concerning life events. As a measure of global stress (not specific to trauma), a 10-item version of the Perceived Stress Scale (Cohen, Kamarck, & Mermelstein, 1983) was used. The scale purports to measure the degree to which situations in one's life are appraised as stressful (e.g., "In the last month, how often have you felt confident about your ability to handle your personal problems?"). The scale is quite internally consistent (a = .84). This global scale was supplemented with a 5-item measure of traumatic stress drawn from the TSS. This scale taps symptoms that are (presumably) more specific to a state of traumatic stress (e.g., easily startled, emotions numb). It also shows adequate internal consistency (a = .76). Because the scale does not require the symptoms to be attributed to specific identifiable stressors, it could be administered to all respondents, including those with no traumatic events. Posttraumatic stress disorder (PTSD). For each person reporting one or more traumatic events, a determination was made of whether he or she had developed a constellation of stress symptoms consistent with a diagnosis of PTSD. In addition to establishing that a traumatic event has occurred (often referred to as Criterion A), the American Psychiatric Association's (1987) Diagnostic and Statistical Manual of Mental Disorders, 3rd ed., rev. (DSAf-III-R) requires that three other criteria be met (B, C, and D) before a diagnosis of PTSD is made. Although it is not a diagnostic instrument, the TSS includes nine questions relevant to Criteria B-D. Five of these questions constitute the traumatic stress scale described previously. Four additional questions (per event) complete the set. Unlike the first five questions, these four do require that a specific attribution to an event is made and thus are asked only when an event-occurrence question elicits an affirmative response. The measure is therefore applicable only to persons who have experienced a traumatic event. Criterion B is the reexperiencing of the trauma. In the present study, this criterion was met if the respondent answered "sometimes," "fairly often," or "very often" to at least one of the following questions: "Since the event, how often have you thought about it when you didn't mean to?" "How often have you had nightmares about this event?" and "Since the event, how often have things you have seen or heard suddenly reminded you of it?" Criterion C encompasses avoidance, hopelessness, and a numbing of responsiveness to the external world. Here, this criterion was met if the respondent answered at least "sometimes" to three or more of the following questions: "In the last month, how

often were your emotions kind of numb?" "How often did you quit caring about people or lose interest in things you used to enjoy?", "Since the event, how often have you avoided situations that remind you of it?", and "In the past 4 weeks, how often were you distressed by feeling hopeless about the future?" This last item was supplied by the Brief Symptom Inventory (BSI; Derogatis & Spencer, 1982) rather than the TSS. (BSI items also have a 5-point response format; the person had to be at least moderately distressed for this item to count.) Criterion D encompasses a varied collection of symptoms indicative of increased arousal. The TSS provided questions relevant to three of these symptoms: "How often were you jumpy or easily started?", "How often did you have trouble sleeping?", and "How often did you become unusually forgetful or have trouble concentrating?" The BSI provided two questions ("feeling annoyed or easily irritated," "temper outbursts you could not control") that were combined to reflect the irritability/anger aspect of Criterion D that is not tapped by the TSS. Of these four indicators of increased arousal, two had to be present for Criterion D to be satisfied. PTSD was scored as present (1) if all criteria were satisfied, absent (0) otherwise. One issue with this measure of PTSD should be considered at the outset. In retrospect, it would have been better if each symptom question had been oriented to the past month alone. The TSS was originally intended for recent events only, and thus the four items that followed events began, "Since the event," whereas the five items located earlier in the interview began, "In the past month." Nonetheless, reliability analyses suggested that the items could work together as a single measure of current PTSD. A scale based on all nine items was as internally consistent (a = .75) as was the scale based on the five "past-month" items only (a =. 76). All nine items contributed to the total scale alpha. Moreover, these alphas did not differ between respondents having recent (past-year) events (a = .73) and respondents having earlier events (a =.76). Results Event Occurrence Total sample frequencies. Table 1 displays lifetime and pastyear frequencies for each event. Lifetime frequencies for the total sample ranged from 4.4% for sexual assault to 30.2% for tragic death (i.e., loss of a loved one by homicide, suicide, or accident). Of those deaths, 3% involved spouses, 6% involved children, 9% involved parents, and 82% involved someone else. Robbery and injury-causing motor vehicle crashes were also quite common, each occurring to about one fourth of these respondents at some point during their lives. Excluding Hurricane Hugo, 69% of this sample had at least one of these events at some point in their lives. In the past year alone, 21% of the sample experienced a violent event. Other hazard (i.e., not Hugo) and robbery were the most frequent events (each occurring to about 6% of the sample). Over this interval, fire and sexual assault were the least frequent (each occurring to less than 1%). Subsample frequencies. Table 1 also presents lifetime and past-year frequencies for each subsample. Generally, events maintained their same rank order of frequency across the groups. Combat, an event experienced only by men, and generally by older men, was an exception. Sex differences in lifetime frequencies (as evidenced by chisquare tests) were as expected. Although women were more likely to have been sexually assaulted, men were more likely to have been in motor vehicle crashes, to have been physically

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FRAN H. NORRIS

Table 1 Lifetime and Past-Year Frequencies of Traumatic Events by Sex, Race, and Age Total

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Event Robbery Lifetime Past-year Physical assault Lifetime Past year Sexual assault Lifetime Past-year Fire Lifetime Past-year Other disaster" Lifetime Past-year Other hazard3 Lifetime Past-year Tragic death Lifetime Past-year Motor vehicle crash Lifetime Past-year Combat Lifetime Past-year Any event" Lifetime Past-year

Male

Female

Black

White

Younger

Middleaged

Older

%

SE

%

SE

%

SE

%

SE

%

SE

%

SE

%

SE

%

SE

24.9 5.9

1.4 0.7

26.2 4.8

2.0 1.0

23.8 6.9

1.9 1.1

29.7 7.0

2.0 1.1

20.3 4.8

1.8 1.0

24.1 6.6

2.2 1.3

26.8 6.5

2.5 1.4

24.1 4.6

2.4 1.2

15.0 2.4

1.1 0.5

18.7* 1.7

1.8 0.6

11.7 3.1

1.4 0.8

18.4* 2.2

1.7 0.7

11.6 2.6

1.4 0.7

19.1* 4.6*

2.1 1.1

16.8* 2.3*

2.1 0.8

8.6 0.0

4.4 0.4

0.7 0.2

1.3 0.6

0.5 0.4

7.3* 0.2

1.1 0.2

4.2 0.4

0.9 0.3

4.6 0.4

0.9 0.3

6.6* 0.5

1.3 0.4

4.5* 0.6

1.2 0.5

1.9 0.0

1.6 — 0.8 —

11.0 0.6

1.0 0.2

10.1 0.2

1.4 0.2

11.9 1.0

1.4 0.4

12.4 0.4

1.5 0.3

9.6 0.8

1.3 0.4

9.3 0.5

1.5 0.4

12.3 1.0

1.9 0.6

11.7 0.3

1.8 0.3

13.3 1.8

1.1 0.4

12.6 1.9

1.5 0.6

14.0 1.7

1.5 0.6

21.8* 2.6

1.9 0.7

4.6 1.0

0.9 0.4

10.4 2.7

1.6 0.9

17.7* 1.6

2.2 0.7

12.3 0.9

1.8 0.5

15.2 6.3

1.1 0.8

15.1 5.7

1.6 1.1

15.3 6.9

1.6 1.1

23.6* 9.4*

1.9 1.3

6.8 3.2

1.1 0.8

15.8 6.3

1.9 1.3

17.7 6.5

2.2 1.4

12.0 6.2

1.8 1.3

30.2 4.9

1.5 0.7

30.0 4.4

2.1 0.9

30.4 5.4

2.0 1.0

36.3* 4.0

2.2 0.9

24.1 5.8

1.9 1.0

33.1 8.5*

2.5 1.5

31.3 3.5

2.6 1.1

25.9 2.2

2.4 0.8

23.4 2.6

1.3 0.5

27.9* 3.4

2.0 0.8

20.1 1.9

1.8 0.6

23.2 1.6

1.9 0.6

23.5 3.6*

1.9 0.8

24.0 4.1

2.2 1.0

26.5 2.3

2.5 0.8

19.8 1.2

2.2 0.6

9.2 0.0

0.9 —

19.3* 0.0

1.8 —

0.0 0.0

— —

9.4 0.0

1.3 —

9.0 0.0

1.3 —

0.5 0.0

0.4 —

7.7 0.0

1.5 —

20.4* 0.0

2.2 —

69.0 21.0

1.5 1.3

73.6* 19.5

2.0 1.8

64.8 22.4

2.1 1.8

76.8* 23.4

1.9 1.9

61.2 18.5

2.2

66.9 27.0*

2.3 2.3

71.6 21.0*

2.3 2.3

68.8 14.2

2.6 1.9

1.7

Note, dash = not applicable. * Excludes Hurricane Hugo. * Frequency significantly greater than counterpart, p < .05.

assaulted, or more generally to have experienced a violent event. No sex differences were found in past-year frequencies of these same events. Race differences were plentiful. Over the course of their lives, Whites were significantly more likely than Blacks to have experienced these events, especially robbery, physical assault, tragic death, or a disaster or hazard other than Hugo. This was true although Whites were far more advantaged socioeconomically: for education, F(l, 994) = 194.98, p < .001; for occupational status (Hollingshead & Redlich, 1958), F(l, 984) = 277.48, p < .001. The one difference that emerged for past-year frequencies, however, was in the opposite direction: Blacks had been more likely to experience a motor vehicle crash during that time. A strong trend was for past-year exposure to decrease with age. This trend also held for certain lifetime frequencies. Only 9% of older adults reported having been physically assaulted in their lifetimes compared with 19% and 17% of younger and middle-aged adults, respectively. Sexual assault showed a similar pattern. Middle-aged adults were the most likely age group to have sustained injuries or property damages due to weather or disaster within the past year.

For methodological rather than substantive reasons, differences in the frequencies of these events across cities were also examined. The occurrence of Hurricane Hugo could have increased the incidence of other violent events, thus producing frequencies that would be inflated relative to other places and times. However, although there were significant differences between cities (for lifetime: x2 (3, N= 1,000) = 13.43, p < .01; for past-year, x2 (3, N = 1,000) = 55.78, p < .001), they could not be attributed to the hurricane. Savannah and Charlotte had higher event frequencies (respectively 75 and 73% for lifetime; 38 and 17% for past-year) than did Greenville and Charleston (respectively 62 and 65% for lifetime; 15 and 13% for past-year).

Event Impact The impact of events was assessed in two ways: by examining the mean levels of stress among those with and without events and by considering the proportions of various groups who met criteria for PTSD (current prevalence). For this purpose, four categorical variables were created. Lifetime crime was scored such that persons who had experienced robbery, physical assault, or sexual assault in the past year received a score of 2,

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EPIDEMIOLOGY OF TRAUMA

persons who had earlier experienced any of the same events received a score of 1, and persons who had never experienced any of these events received a score of 0. Lifetime hazard was scored such that persons who had experienced a fire, disaster, or hazard in the past year received a score of 2, persons who had earlier experienced any of these events (including Hurricane Hugo) received a score of 1, and persons who had never experienced any of these received a score of 0. Similarly, lifetime accident was scored 2 given past-year motor vehicle crashes or tragic deaths, 1 given earlier events, and 0 given no events. Finally, any event was scored 2 given past-year occurrences of any of the above events, 1 given earlier events (including Hugo and combat), and 0 given no events. Respondents could receive non-0 scores on as many of these variables as warranted by their event histories. Although some precision was lost in creating aggregate event measures, this procedure assured that the number of persons within each category was sufficient to provide stable means and frequencies at the subgroup level (see Table 2). Differences in stress means. Mean differences were tested using analysis of variance (ANOVA) with a 2 X 2 x 3 x 3 (Sex X Race X Age X Event) between-subjects factorial design. All three demographic factors had main effects on global stress: for sex, F(\, 955) = 14.66, p < .001; for race, F(l, 955) = 5.16, p < .05; for age, F(2, 955) = 14.35, p < .001. The direction of these effects was such that, on the average, higher stress was exhibited by female, White, and younger adults. On traumatic stress, main effects were again found for sex, F(l, 955)=10.71,p< .001, and race, F(l, 955) = 5.23, p < .05, but not for age. The major purpose of this analysis was to identify the main and interactive effects of violent events on the stress measures. The analyses were repeated four times, once for each event aggregate. In the first analysis, lifetime crime was the event measure. It had significant main effects on both global stress, F(2, 955) = 4.53, p < .01, and traumatic stress, F(2,955) = 7.45, p < .001. The effect was linear in character, f(955) = 3.22, p < .001, with the highest means exhibited by the past-year group and

the lowest exhibited by the never group. The interaction of Event X Race was also significant for global stress, F(2,955) = 4.06, p < .05, and it approached significance for traumatic stress, F(2, 955) = 2.38, p < .09. Among Whites, the means obtained by never, earlier, and past-year groups differed little from one another, but among Blacks they differed strongly and were highest for the past-year group. For global stress only, there was also an Age X Event interaction, F(2,955) = 2.65, p < .05. Older adults usually showed lower levels of stress than others, but in the presence of past-year crimes each age group showed high and comparable levels of stress. The effects of hazard exposure appeared to be more limited than those of crime. Lifetime hazard had no effect on global stress. However, this experience was associated with more traumatic stress, F(2,955) = 3.84, p < .01. This trend was quadratic in form, /(955) = -2.02, p < .05. That is, means were highest among those in the earlier group, which included (but was not limited to) victims of Hurricane Hugo. There was also a 3-way interaction of Hazard X Sex X Race, F(2,955) = 3.89, p < .05. A further breakdown of the means showed that Black men were the only group to show higher stress following past-year hazards than earlier hazards. Lifetime accident had main effects on both measures: for global stress, F(2, 955) = 8.79, p < .001; for traumatic stress, F(2, 955) = 7.56, p < .001. Means were in all cases higher among persons who had experienced either a tragic death or injury-causing crash than among those who had not. As found for crime, the effect was generally linear in nature, £(955) = 2.58, p < .01; means were highest in the past-year group and lowest in the never group. In addition to the main effect of accident, there was a significant Age X Event interaction for global stress, F(4, 955) = 2.61, p < .05. Among middle-aged adults only, the means of those with earlier events exceeded those with past-year events. There was also a significant 3-way Sex X Race X Event interaction on both global stress, F(2, 955) = 3.27, p < .05, and traumatic stress, F(2, 955) = 4.01,

Table 2 Distributions of Aggregate Event Measures by Sex, Race, and Age Total

Male

Female

White

Black

Younger

Middle-aged

Older

663 248 80

310 132 32

353 116 48

301 149 44

362 99 36

235 89 39

198 83 26

230 76 15

320 588 83

155 283 36

165 305 47

109 324 61

211 264 22

124 206 33

90 191 26

106 191 24

553 365 74

256 183 36

297 182 38

252 215 27

301 150 46

195 123 45

165 125 18

193 117 11

Never Earlier" Past-year

149 633 209

64 318 92

85 315 117

43 334 117

106 299 92

53 211 99

48 195 64

48 227 46

Total

991

474

517

494

497

363

307

321

Event Crime Never Earlier

Past-year Hazard Never Earlier1 Past-year Accident Never Earlier

Past-year Any event

* Includes Hurricane Hugo.

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414

FRAN H. NORRIS

p < .05. On both scales, effects of events were strongest among Black men. Any event had main effects on both global stress, F(2,955) = 3.16, p < .05, and traumatic stress, F(2, 955) = 6.62, p < .001. Means were highest given past-year events, and lowest given no events, t(955) = 2.42, p < .05. Consistent with previous analyses, effects of events were again strongest among Black men. However, the 3-way Sex X Race X Event interaction did not quite achieve statistical significance, F(2, 955) = 2.64, p < .07. Differences in stress rates. Stress may be conceptualized as either a continuum or as a condition. In the previous analyses, stress was measured as the former; it was assumed that all individuals, both with and without traumatic events, experience some degree of stress. Another way to assess the relative stressfulness of these events, as well as the relative vulnerability of different demographic groups, is to consider the proportions of victims who met criteria for a diagnosis of posttraumatic stress disorder (PTSD). For lifetime occurrences and the total sample, it was possible to establish the proportion of people who satisfied diagnostic criteria for each specific event (e.g., physical assault). Because of the smaller «s available for past-year occurrence and demographic subsamples, for them these proportions could be reliably established only for the aggregate event categories (e.g., crime). It should be recalled that these figures relate to current symptoms, not lifetime prevalence. These rates are presented in Table 3. Rates of current disorder varied according to the nature of

the event. The lowest rate (2%) was associated with combat, the highest (14%) with sexual assault. Rates for physical assault (13%) and motor vehicle crash (12%) were not far behind. Hazards, robbery, and tragic death showed rates intermediate to these extremes, ranging from 5 to 8%. The rate for tragic death did not vary depending on whether the loss was that of a parent, spouse, or child or of someone else close. Among the total group of respondents exposed to a violent event, about 7% exhibited PTSD. In contrast to the findings concerning levels of stress, very little variability in rates of stress was accounted for by the recency of events. Recency effects were overshadowed by severity. Because sample frequencies are generally less stable than sample means, it is difficult to establish with confidence whether any observed sex, race, and age differences were reliable. For any event, women showed a current rate about 40% higher than men, but the difference was not statistically significant, x2 (1, N = 848) = 1.89, p < .17. In the case of crime, however, this difference was strong and statistically reliable, x2 (l,N= 329) = 3.92, p < .05; here, women showed a rate of PTSD more than twice (12%) that exhibited by men (6%). In contrast to the findings regarding the continuum of stress, race did not predict the presence of severe stress. Because the ANOVAs suggested the presence of a three-way Race X Sex X Event interaction, the proportions showing PTSD given any event were also broken down by sex and race. There were no differences by race within sex (or vice versa). Age was by far the strongest predic-

Table 3 Percentage of Event Samples Meeting All Criteria for Current PTSD Type of event

Total

Male

Female

White Black

Crime By time Past-year Earlier By event Robbery Physical assault Sexual assault Hazard By time Past-year Earlier By event Fire Hurricane Hugo Other disaster Other hazard Accident By time Past-year Earlier By event Tragic death Motor vehicle crash Combat Any event Excluding Hugo Including Hugo

8.5

5.5

11.5*

7.2

5.0

6.5

7.3

6.0 6.1

Younger

Middle-aged

Older

10.4

7.8

13.6

3.3*

5.1

6.9

6.6

6.4

4.1

10.0

8.2

9.2

9.5

11.7

3.9*

8.8 8.5

7.6 7.5

7.2 7.1

9.0 9.0

9.9 8.8

3.1* 4.0*

11.3 7.6 6.0 13.3 13.6 5.8 4.8 5.9 6.4 4.9 5.3 6.6 8.6 9.5 8.4 7.6 11.5 2.2 7.4 7.3

Note. PTSD = posttraumatic stress disorder. For sample ns, see Table 2 of this article. * Significantly different from rate of counterpart, p < .05.

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EPIDEMIOLOGY OF TRAUMA

tor; older persons showed consistently lower rates of PTSD, especially with regard to crime and accident. In the total sample of 1,000, 51 persons (5.1%) satisfied all four criteria (A-D) for current PTSD for reasons other than exposure to Hurricane Hugo. When cases that could be attributed specifically to Hugo were also included, this number expanded to 62 (6.2%). Fifteen persons satisfied all criteria for both Hugo and some other event. The proportions currently meeting DSM-III-R criteria were primarily determined by Criterion C. For example, 83% of Hurricane Hugo victims met Criterion B (one or more intrusion symptoms), and 42% met Criterion D (two or more arousal symptoms); but only 6% met Criterion C (three or more numbing symptoms). Figures are low for Criterion C because three separate symptoms must be shown. After Hugo, 40% showed at least one Criterion C symptom, and 16% showed at least two. Table 4 presents comparable statistics for each specific event (lifetime occurrence).

Discussion This sample was not drawn randomly, nor is it strictly representative of the general population. Estimates are therefore subject to unknown biases. Nonetheless, a few conclusions regarding the approximate and relative frequencies of various events may cautiously be drawn.

Exceeding even those reported by Breslau et al. (1991), the overall frequencies with which these events occurred to these normal, community-residing adults were striking. Of the 1,000 persons in this sample, more than 200 had some type of violent encounter in the past year alone. It could be argued that this rate is unduly high because of the tendency to telescope memories of events into the recent past. Although this may be the case, the occurrence of Hurricane Hugo at the point one year ago may have helped to protect against this threat. Landmarks or markers, such as natural disaster, have been found to improve the accuracy of temporal judgments in reporting past experiences (Loftus & Marburger, 1983). It is also apparent from this study that risks that are small on an annualized basis have a way of accumulating over the years into probabilities that are quite sizable. For example, as Table 1 shows, in any given year, fewer than 1 in 100 persons may be victimized by fire. \fet, over the lifetime, this probability grows to more than 1 in 10. Similarly, within a year's time, about 1 in 50 adults may experience a serious motor vehicle crash. Sizable in itself, this figure pales beside the observation that 1 in 4 will experience this event at some point in their lives. Sooner or later, these data suggest, we are more likely to experience than not to experience a traumatic event. Is this fact significant from a mental health perspective? With two qualifications, one methodological and one more substantive, I believe the answer to this question is yes. First, present

Table 4 Percentage of Event Samples Showing Criterion Symptoms Event Robbery Physical assault Sexual assault Fire Hurricane Hugo Other disaster Other hazard Tragic death Motor vehicle crash Combat

No. of Symptoms 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more 1 or more 2 or more 3 or more

Criterion B (Intrusion)

Criterion C (Numbing)

Criterion D (Arousal)

67.4 46.1 9.6 67.9 46.6 17.3 93.3 72.8 27.3 60.9 37.3 10.9 82.5 51.3 4.4 54.8 24.0 6.0 51.9 27.6 4.6 76.2 60.0 10.3 64.9

59.9 21.7 6.8 73.3 31.3 16.0 84.0 43.1 13.6 56.3 20.8 6.3 39.5 15.5 6.0 39.2 15.9 7.6 42.0 19.0 7.2 50.0 20.2 8.9 59.3 29.0 13.6 37.0 9.8 2.2

74.3 44.2 21.7 77.4 53.4 28.7 88.7 68.2 40.9 74.6 47.3 20.9 68.6 42.3 19.6 69.9 45.1 21.8 75.7 47.4 22.4 72.9 43.1 22.9 68.8 42.3 24.8 45.7 27.3 10.9

47.4

9.8 67.4 51.1 19.6

Note. Diagnostic criteria for posttraumatic stress syndrome (American Psychiatric Association, 1987).

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416

FRAN H. NORRIS

levels of perceived stress were significantly higher among persons with previous traumatic experiences than among persons who had had no traumatic events. The association was heightened in the case of recent (past-year) events but not limited to them. Unfortunately, this cross-sectional study cannot establish a direct causal link. Perceptions of stress and the occurrence of trauma could each emerge from common causes unidentified here. Stabilities in lifestyle, personality, and environment could easily explain why the same person who experienced trauma in the past is experiencing high stress now. Establishing cause and effect is exceedingly difficult in traumatic stress research where prospective designs are rarely feasible. Notwithstanding the difficulty involved, further progress will depend on our adoption of more innovative strategies that allow us to collect pre-event data as part of our research designs (see Reid, 1990). The second and more substantive qualification relates to the relatively modest size of the trauma effects. With regard to overall levels of perceived stress, these events appear to be only one of many sources of stress in people's lives. Interpersonal relations, financial problems, and the like entail little drama but much stress. The importance of such chronic difficulties has been well documented in previous research (e.g., Lazarus & DeLongis, 1983; McGonagle & Kessler, 1991; Pearlin, Lieberman, Menaghan, & Mullan, 1981). It is not particularly helpful to force an either-or choice about whether acute or chronic demands contribute the most to perceptions of stress. All sources matter, undoubtedly in complex and interconnected ways. With regard to the specific constellation of symptoms that compose PTSD, rates ranged from 2-14% depending on the nature of the event experienced. Excluding Hurricane Hugo, which is specific to this setting, 51 participants in this study (5.1%) satisfied all four criteria for PTSD. These data suggest that the current prevalence of PTSD is in the range of 7-11% among persons who have been exposed to violent crimes, deaths, or accidents and in the range of 5-8% among persons who have been exposed to various environmental hazards. These rates of current disorder given exposure are similar to those reported by Kilpatrick and Resnick (1992) and about one third the level of lifetime rates reported by Breslau et al. (1991). This proportion is in accord with previous findings regarding the ratio of current to lifetime disorder (Green et al., 1990; Kulkaetal, 1990). The proportions of victims who satisfied each of the criteria for PTSD were vastly different. This study was not the first to demonstrate that whether a trauma victim meets DSM-III-R criteria is largely a matter of whether he or she satisfies Criterion C (see Solomon & Canino, 1990). Whatever the intent, the result of the present diagnostic system is that intrusiveness (no matter how pervasive) and arousal (no matter how persistent) are judged clinically insignificant unless a very diverse set of outcomes (encompassing numbing, avoidance, and hopelessness) are also present. All rates reported here would double (and in some cases triple) if two rather than three symptoms were sufficient to satisfy Criterion C. PTSD represents only the tip of the iceberg in terms of experienced distress. Cutpoints may be necessary for diagnosis, but that fact makes them no less arbitrary. In reporting rates of disorder that are constrained to be

low, one should be cautious not to give the mistaken impression that few people become distressed following traumatic events. If one event stood out from the pack, it was motor vehicle crash. This event was less frequent than some (robbery, tragic death) and less traumatizing than some (sexual or physical assault), but when both the frequency and severity data were considered together, it emerged as perhaps the single most significant event among those studied here. At a lifetime frequency of 23% and a PTSD rate of 12% of that, this event alone would yield 28 seriously distressed persons for every 1,000 adults in the United States. This is an interesting observation given how seldom this event has been studied relative to crime, disasters, and bereavement. It is also an event for which issues of cause and effect loom particularly large. Having difficulty sleeping, having trouble concentrating, and being easily startled could easily contribute to the occurrence of accidents as well as result from them. With regard to the relative vulnerability of different demographic groups, no group was immune from either trauma or stress. Women were more exposed to sexual assault, whereas men were more exposed to physical assault. Women generally perceived their lives as more stressful, and, given the occurrence of violent crime, they were more likely to satisfy diagnostic criteria for PTSD. This greater vulnerability of women is consistent with previous studies that have specifically focused on PTSD (Breslau et al., 1991; Helzer et al., 1987). However, it does not appear to hold for all symptom outcomes across specific traumatic events (Phifer, 1990; Solomon, Smith, Robins, & Fischbach, 1987). The most complex pattern of findings involved race. Compared with Blacks, Whites reported more occurrences of physical assault and tragic deaths, as well as of disasters and hazards other than Hurricane Hugo. These data are not consistent with previous reports (U.S. Department of Justice, 1992). The difference is because so many Whites reported events (e.g., 19% reported an assault) rather than because too few Blacks did so (12% reported an assault). Perhaps urban southern Whites are more subjected to violence than their counterparts in suburbia or other parts of the nation. The relative vulnerabilities of the two subsamples changed when impact was being considered. Race differences in extreme stress were insignificant, but race differences in stress levels were quite strong. Given the occurrence of events, Blacks —and especially Black men—exhibited the highest levels of stress. Existing literature on trauma among civilian Black Americans is meager (Neal & Turner, 1991), and that which exists is contradictory or indicative of extremely complex effects. In the Buffalo Creek Study, for example, Blacks were initially less traumatized (Gleser, Green, & Winget, 1981), but a disproportionate number exhibited delayed-onset PTSD (Green et al., 1990). This pattern, which arose because of some unique social dynamics, highlights the importance of specifying the cultural context in which traumatic events occur. This is an exceedingly difficult task for epidemiological studies. In the present setting, three potential explanations for Blacks' greater vulnerability can be offered. They are not mutually exclusive. One is that the events experienced by Blacks were fewer in number but more serious in nature. As is well documented in

417

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EPIDEMIOLOGY OF TRAUMA studies of rape (e.g, Ellis, Atkeson, & Calhoun, 1981; Sales, Baum, & Shore, 1984), one assault is not necessarily the same as another. Nor are two individuals' experiences in a disaster or fire necessarily the same (Lindy, Green, & Grace, 1987). Unfortunately, these data do not allow the relative severity of events of the same type to be quantified. The second explanation of the race effect relates to the greater economic resources enjoyed by Whites. Whether the event under study is traumatic (e.g., Phifer, 1990) or more ordinary (Kessler & Cleary, 1980; Liem & Liem, 1978; Thoits, 1982), there is substantial evidence that social status buffers the impact of life events. The third possibility, related to the second, is that minorities may confront hostility, prejudice, and neglect, which serve to heighten the effects of a crisis (Kaniasty & Norris, 1991; Moritsugu & Sue, 1983; Penk & Allen, 1991). Age differences were generally in the direction of lower frequencies among older people. As such, this finding is consistent with the literature regarding age differences in the distributions of more normative life events (e.g., Hughes, Blazer, & George, 1988; Masuda & Holmes, 1978). This trend toward fewer events was much stronger for past-year frequencies than for lifetime frequencies. If risks do accumulate over time, one might expect older people to have higher lifetime frequencies than younger or middle-aged adults, but they did not. Two explanations for this pattern can be offered. One is a cohort effect. For example, if the young are more prone to violence, and if this is more true now than in previous decades, then older people would have lower exposure rates even though they have lived through more years. The second explanation is a reporting effect. Perhaps memories of even quite serious events fade over time. Although there is some evidence for the lawful forgetting of life events (Cohen, 1988; Jenkins, Hurst, & Rose, 1979), more salient events may be exempt from these effects (Punch & Marshall, 1984). However, if events were forgotten, or simply judged too insignificant to mention, estimates of the prevalence of PTSD among those exposed would be inflated. Unfortunately, such errors are probably not limited to older adults. Where exposure was acknowledged, older people fared better, especially in terms of proportions satisfying PTSD criteria. Their low rates of PTSD given exposure may, in fact, argue against the possibility that they reported only their most significant life events. The age effect is consistent with previous observations that people may develop resilience to stress over the course of their lives (Norris & Murrell, 1987; 1988). Or, it may simply reflect a greater average passage of time since the events occurred. Past-year crime was a clear exception to the general rule of better outcomes among older adults. Few older adults had these events, but those who did showed levels of stress comparable to those shown by younger and middle-aged adults. Conclusions based on these findings must be qualified by several methodological limitations. A sample more precisely representative of the general population, pre-event measures of stress, and more detailed data on the events experienced are all features that would have improved the study greatly. Although another potential problem is the self-report nature of the study, Solomon, Mikulincer, and Hobfoll (1987) have demonstrated reasonably good agreement between PTSD diagnoses made by clinicians and those based on self-report scales. More generally,

the present study should be judged relative to the state of the art, which has provided little data of epidemiologic value. Although nonrandom, this sample was quite heterogeneous, being drawn from 12 distinct neighborhoods across four midsized cities. Half Black and half White, half male and half female, including younger, middle-aged and older persons, the sample does approximate the diversity found in the southeastern United States. Therefore the data can be instructive—if not definitive—about the relative frequency and severity of various traumatic events.

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