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Low specificity of symptoms on the post-traumatic stress disorder (PTSD) symptom scale: A comparison of individuals with PTSD, individuals with other anxiety disorders and individuals without psychopathology

Iris M. Engelhard1*, Arnoud Arntz2 and Marcel A. van den Hout1 1Clinical and Health Psychology, Utrecht University, Utrecht, The Netherlands 2Department of Medical, Clinical and Experimental Psychology, Maastricht University, Maastricht, The Netherlands

Objectives. Screening for post-traumatic stress disorder (PTSD) takes place in clinical and research settings where diagnostic interviews are not feasible, and typically relies on self-report instruments like the PTSD symptom scale (PSS). Concerns have been raised about the specificity of PTSD symptoms assessed by questionnaires. This study examined whether the PSS distinguishes between patients with PTSD and those with other anxiety disorders or healthy controls.

Design. A between-participants design was employed.

Methods. The participants were 65 individuals with PTSD, 40 individuals with other anxiety disorders and 40 healthy controls. They completed the PSS with respect to a range of stressful life-events.

Results. Using this instrument, 86% of individuals with PTSD and 5% of healthy controls endorsed sufficient symptoms to meet the PTSD diagnosis. This was also the case for 43% of individuals with other anxiety disorders, and self-reported symptoms related to traumatic events and aversive events that are generally not considered traumatic.

Conclusions. The findings suggest that many people screened positive for PTSD may actually be suffering from another anxiety disorder.

Post-traumatic stress disorder (PTSD) was established as a psychiatric diagnosis in the

DSM-III (American Psychiatric Association, 1980) and defined as a characteristic

symptom pattern following exposure to a traumatic event. This includes persistently

* Correspondence should be addressed to Iris M. Engelhard, Clinical and Health Psychology, Utrecht University, PO Box 80140, 3508 TC Utrecht, The Netherlands (e-mail: [email protected]).

The British Psychological Society

449

British Journal of Clinical Psychology (2007), 46, 449–456

q 2007 The British Psychological Society

www.bpsjournals.co.uk

DOI:10.1348/014466507X206883

re-experiencing the event, avoidance of its reminders and numbing, and hyperarousal

(American Psychiatric Association, 1994). The establishment of PTSD has brought about

an outburst of research and clinical work, but there has been much debate about the

validity of the diagnosis. There are at least two main concerns: that traumatic stressors

do not form a unique class with their own distinctive effects (e.g. Bowman, 1999;

McNally, 2003; Scott & Stradling, 1994; Yehuda & McFarlane, 1995) and that PTSD is not clearly distinct from existing disorders (e.g. Brewin, 2003) or normal trauma-related

reactions (Summerfield, 2001).

PTSD as a condition or psychiatric syndrome is unique in that it is thought to result

from a particular kind of event, which is defined in the DSM-IV as ‘actual or threatened

death or serious injury, or a threat to the physical integrity of self and others’, which

evokes ‘intense fear, horror, or helplessness’ (p. 429). However, the risk of depression

and other anxiety disorders is also increased after such events (e.g. Breslau, 1998; Shalev

et al., 1998), and several studies have reported that substantial PTSD symptoms can also arise from relatively minor (ordinary) stressors, such as problems with work, finances

and relationships (e.g. Mol et al., 2005; Scott & Stradling, 1994; Solomon & Canino,

1990). Furthermore, several PTSD symptoms overlap with other anxiety disorders and

depression (McNally, 1992). Involuntary intrusive memories are often considered its

hallmark symptoms (e.g. Jones & Barlow, 1990), but these also occur in panic disorder

(Rainey, Aleem, Ortiz et al., 1987), social phobia (Hackmann, Clark, & McManus, 2000)

and depression (Reynolds & Brewin, 1999).

In clinical or research settings, self-report PTSD instruments, like the PTSD symptom scale (PSS; Foa, Riggs, Dancu, & Rothbaum, 1993), may be used for rapid screening by

deciding whether or not participants meet symptom criteria for PTSD (see e.g. Brewin,

Andrews, & Rose, 2000; Ehlers, Mayou, & Bryant, 1998; Engelhard, van den Hout,

Arntz, & McNally, 2002; Hoge, Castro, Messer et al., 2004; Schlenger, Caddell, Ebert

et al., 2002). It is relevant to know whether a self-report measure of PTSD symptoms,

like the PSS, distinguishes between patients with PTSD and those with other anxiety

disorders. The prevalence of all other anxiety disorders is more than twice that of PTSD.

If other anxiety patients also commonly report symptoms on PTSD instruments, this could imply that many individuals screened positive for PTSD in population research are

actually suffering from another anxiety disorder.

The aim of this study was to assess the specificity of self-rated PTSD symptoms on the

PSS in a sample of PTSD patients, other anxiety disorder patients and individuals without

psychopathology. The groups were matched on background factors that are related to

the presence of anxiety disorders (i.e. age, sex and socio-economic factors; see Kessler

et al., 1994). We tested whether self-rated PTSD symptoms were common among

patients with PTSD and equally uncommon among patients with other anxiety disorders and healthy controls.

Method

Participants The participants were 65 individuals with PTSD (40 women; 63%), 40 had other anxiety

disorders (24 women; 60%) and 40 were healthy controls (24 women; 60%). Current

comorbid axis I diagnoses, diagnosed by means of the structured clinical interview for

axis I DSM-IV disorders (SCID-I; First, Spitzer, & Williams, 1997), in the PTSD group

included 9 major depression, 3 dysthymia, 10 panic disorder, 5 social phobia, 3

450 Iris M. Engelhard et al.

obsessive–compulsive disorder, 1 generalized anxiety disorder, 9 specific phobia and 2

hypochondriasis (some PTSD participants had more than one comorbid disorder). The

primary diagnoses of patients with other anxiety disorders were 21 panic disorder, 10

social phobia, 6 obsessive–compulsive disorder, 2 generalized anxiety disorder and 1

specific phobia. None of them had comorbid PTSD, and none of the healthy controls

exhibited a SCID-I diagnosis. The mean age was 34 (SD ¼ 11). Most participants were married or cohabiting, 19% were single and 10% were divorced. Almost half was college

educated. About one-third was employed, one-third was unemployed and the others

were student or homemaker. These factors were not significantly different between the

groups (smallest p ¼ :07, for education). The mean period of pre-treatment complaints was 4 years (SD ¼ 8) for PTSD patients and 7.1 years (SD ¼ 8:7) for patients with other anxiety disorders.

Procedure and measures Patients admitted for treatment to the Anxiety Disorders Program of the Community

Mental Health Centre of Maastricht, which is affiliated with Maastricht University, were

administered the SCID-I by a licensed psychologist with extensive diagnostic

experience. They received verbal and written information about the study and were

invited to participate. After giving written informed consent, they completed the PSS-

self-report version (Foa et al., 1993), State-Trait Anxiety Inventory (STAI; Spielberger, 1983), Symptom Checklist-90 (SCL-90; Derogatis, 1977) and Fear Questionnaire

(FQ; Marks & Mathews, 1979). The healthy controls were recruited from the community

with advertisements seeking healthy persons for a study of questionnaires. They

received verbal and written information about the study. After giving written informed

consent, they were administered the SCID-I by a licensed psychologist and the

questionnaires, except the SCL-90. An Institutional Review Panel approved this study.

The PTSD group rated the PSS with respect to their most traumatic event, which was

consistent with the SCID-I-PTSD module. Participants without PTSD were asked to identify their most bothersome, aversive life-event, and to rate the PSS with respect to

this event. Respondents rated how much each symptom had bothered them in the past

month, using a four-point scale (0, not at all; 3, almost always). Self-rated symptoms

based on the PSS agreed with the PTSD module of the SCID-I (First et al., 1997) for

62–90% of victims with PTSD and 84–100% of victims without PTSD (Foa et al., 1993;

Wohlfarth, van den Brink, Winkel, & ter Smitten, 2003). The PTSD diagnosis was

calculated according to the DSM-IV symptom criteria. Foa et al. (1993, 1997) scored a

symptom as present if it was rated at least 1 (‘once in a while’), but some researchers (e.g. Brewin et al., 2000; Engelhard et al., 2002) used a more conservative scoring rule of

at least 2 (‘half the time’). In this study, both scoring rules were used. Cronbach’s alpha

was 0.85 for the PTSD group and 0.95 for all groups. Subscale coefficients for re-

experiencing, avoidance and hyperarousal were 0.85, 0.73 and 0.76, respectively, for

the PTSD group, and 0.92, 0.88 and 0.86, respectively, for all groups.

Results

Traumatic events reported by the PTSD group were physical (N ¼ 22) or sexual assault (N ¼ 18), accident (N ¼ 14), witnessing violence or death (N ¼ 4), war (N ¼ 2) and other (N ¼ 5; i.e. almost choking on food, catching fire from fondue, being briefly jailed

Specificity of symptoms on the PSS 451

on an alleged child sexual abuse charge, death of a child and neonatal death). The most

aversive events reported by other anxiety patients were death of loved one (N ¼ 8), witnessing or experiencing violence (N ¼ 5), somatic illness of self or loved one (N ¼ 5), car crash (N ¼ 2), ‘hyperventilation’, panic attack and change in medication (N ¼ 6), aversive social event (N ¼ 3) and other (N ¼ 11; i.e. rape, parents arguing, maggots being thrown at as child by other child, partner’s infidelity, own infidelity, being

bullied, being fired, being overworked, doubts about sexual orientation due to same-sex

childhood sexual experience, being told by relative to be a bad mother and witnessing a

child almost getting hurt on a conveyer belt). The most aversive events reported by

healthy controls were death of loved one (N ¼ 15), accident of self or loved one (N ¼ 8), breakup or divorce (N ¼ 5), somatic illness of loved one (N ¼ 4), undisclosed (N ¼ 1) and other (N ¼ 7; i.e. being at pool during thunderstorm as child, being caught lying as child, briefly losing sight of daughter during family trip, financial problems of

mother, being suspended from High School, being sent to boarding school as teenager

and not becoming a professional soccer player).

Table 1 shows the means (SD) of the psychometric measures. As expected, the groups

with PTSD or other anxiety disorders scored significantly higher on the STAI and FQ than

the healthy controls. For the latter group, the STAI and FQ scores fell in the normal range (Spielberger, 1983; Gillis, Haaga, & Ford, 1995). Compared with the patients with other

anxiety disorders, the PTSD group scored significantly higher on the PSS (subscales).

Contrary to what was hypothesized, the group with other anxiety disorders scored higher

on the PSS (subscales) compared with the healthy controls.

Next, we tested whether the high PSS scores in the group with other anxiety

disorders could be attributed to Criterion A traumatic events (including death of loved

one and panic attack). However, there were no significant differences on the PSS scores

between 20 patients who met Criterion A events [M ¼ 11:9, SD ¼ 9:9] and 20 who did not [M ¼ 17:2, SD ¼ 10:6; Fð1; 38Þ ¼ 2:6, ns]. The difference was in the opposite direction to what would be expected if Criterion A events were related to PTSD

symptoms.

Table 1. Means (standard deviations in parentheses)

Group

Measures PTSD Other anxiety disorders Healthy F

PSS 27.0 (10.8)a 14.1 (10.4)b 2.5 (3.7)c 89.0* Re-experiencing 8.0 (3.9)a 3.5 (3.6)b 0.6 (1.5)c 66.4* Avoidance 10.6 (4.9)a 5.4 (5.0)b 0.6 (1.6)c 68.2* Arousal 8.4 (3.7)a 5.1 (3.1)b 1.4 (1.4)c 68.0* STAI-trait scale 54.3 (12.6)a 52.6 (10.2)a 31.7 (9.3)b 56.6* STAI-state scale 53.6 (13.9)a 47.6 (12.9)a 29.4 (8.4)b 48.5* SCL-90 1.5 (0.8)a 1.2 (0.6)a 1.5 FQ fear 38.2 (21.2)a 44.6 (20.6)a 17.1 (7.1)b 25.6* FQ avoidance 41.5 (24.1)a 42.4 (22.7)a 14.5 (10.3)b 25.1*

Note. Possible ranges of scores were PSS, 0–51; STAI-state/trait, 20–80; SCL-90 global severity index, 0–4; FQ fear/avoidance, 0–120. Means with different subscripts differ significantly at p , :05 in the multiple comparison.

*p , :05.

452 Iris M. Engelhard et al.

Table 2 shows a comparison of DSM-IV PTSD-diagnoses made using the PSS with the

SCID-I. Using the conservative scoring rule and comparing the individuals with PTSD

with individuals with other anxiety disorders, the sensitivity was 0.48 (proportion of

true positives), specificity was 0.8 (proportion of true negatives), positive predictive

value was 0.79 (proportion of people who score positive on the PSS who actually have

PTSD on the SCID-I), negative predictive value was 0.48 (proportion of people who score negative on the PSS who actually do not have PTSD on the SCID-I) and the overall

‘hit rate’ was 0.6. Individuals with other anxiety disorders met the PTSD symptom

criteria on the PSS in relation to ‘hyperventilation’, panic attack, being bullied, heart

attack of father, witnessing brother being hurt in a fight, parents arguing, partner’s

infidelity and being fired. The specificity was 1 for the healthy control group.

Using the liberal scoring rule and comparing the individuals with PTSD with the

individuals with other anxiety disorders, the sensitivity was 0.86, specificity was 0.58, positive predictive value was 0.77, negative predictive power was 0.72 and the overall

hit rate was 0.75. 1 For the further nine patients with other anxiety disorders, PTSD

symptom criteria were met in relation to panic attack (N ¼ 2), change in medication, maggots being thrown at as a child, rape, death of a relative after illness (N ¼ 2), own infidelity and being overworked. Most of them had a primary diagnosis of panic disorder (N ¼ 10) or social phobia (N ¼ 4). The specificity was 0.95 for the healthy controls (two met the PTSD symptom criteria due to death of loved one after illness).

Discussion

PTSD symptoms on the PSS showed good sensitivity and specificity distinguishing PTSD

patients from healthy controls when using the liberal scoring rule, which nicely

replicates earlier findings (Foa et al., 1993, 1997; Wohlfarth et al., 2003). However, with

the same scale and criteria, nearly half of the patients with other anxiety disorders

reported sufficient symptoms to meet the PTSD diagnosis. The conservative scoring

rules out a number of false positives, but the gains in specificity go hand in hand with a

loss of sensitivity. There are several explanations for the high rate of false positives among anxiety

patients without PTSD. First, the aversive events mentioned by many patients without

Table 2. Comparison of diagnoses made using the PTSD symptom scale (PSS) with the structured

clinical interview for axis I DSM-IV disorders (SCID-I)

SCID-I

PSS PTSD Other anxiety disorders Healthy controls

Conservative scoring Positives 31 8 0 Negatives 34 32 40

Liberal scoring Positives 56 17 2 Negatives 9 23 38

1 Recent studies (e.g. Coffey et al., 2006) have suggested a severity cut-off. The findings are similar when using 15 as scoring

rule.

Specificity of symptoms on the PSS 453

PTSD are not typically regarded as traumatic, at least not by the DSM-IV (partner’s

infidelity, being overworked, etc.), but may breed symptoms that characterize PTSD. As

mentioned, earlier studies have documented PTSD symptoms after problems with work,

finances and relationships (e.g. Mol et al., 2005). Second, there is considerable overlap

between symptoms of PTSD and other anxiety disorders. Four of the five PTSD

hyperarousal symptoms are also defining features of generalized anxiety disorder, and the PTSD numbing symptoms (e.g. ‘feeling detachment or estrangement from others’)

are similar to derealization and depersonalization in panic disorder. Some of the DSM-IV

PTSD symptoms refer to the traumatic event (e.g. intrusions about the trauma), but

many others do not (i.e. ‘diminished interest or participation in significant activities’,

‘feeling detachment or estrangement from others’, ‘restricted range of affect’, ‘sense of a

foreshortened future’, ‘difficulty falling or staying asleep’, ‘irritability or outbursts of

anger’, ‘difficulty concentrating’, ‘hypervigilance’ and ‘exaggerated startle responses’;

American Psychiatric Association, 1994, pp. 424–429). Research among traumatized individuals has shown that the most sensitive (PSS) symptoms are those of the

hyperarousal cluster, intrusive recollections, distress when confronted with reminders

and cognitive avoidance. However, these show low to moderate specificity (Ehlers et al.,

1998). Anxious patients without DSM-IV-defined trauma might endorse many of those

items. An example could be an OCD patient with harming obsessions affirming that

(s)he has intrusions about a traumatic event. The high rate of false positives may be due

to symptom overlap or symptoms being so similar that anxiety patients without PTSD

overlook subtle differences and affirm their presence. Third, several symptoms of avoidance/numbing and hyperarousal are prominent in depression (McNally, 1992).

Clinical or subclinical depression often co-occurs with anxiety disorders, including

PTSD (Brown, Campbell, Lehman, Grisham, & Mancill, 2001). The high rate of false

positives among other anxiety patients could result from symptom overlap with

(subclinical) depression. Finally, neuroticism is a fundamental personality trait that

increases risk of anxiety disorders and/or depression (Clark, Watson, & Mineka, 1994).

In fact, neuroticism scores of clinical patients are about two standard deviations above

the population mean (Van den Hout, 2004). Interestingly, the symptom overlap between neuroticism and the PTSD hyperarousal symptoms is considerable (Engelhard, van den

Hout, & Kindt, 2003). Thus, shared variance between anxiety disorders and neuroticism

might be responsible for the high rate of false positives.

Whatever the reason for the high rate of false positives, its existence is troublesome.

The PTSD diagnostic criteria are unusual by including an etiological factor (a particular

traumatic event). The validity of the diagnosis does not seem to benefit from this: most

individuals exposed to a DSM-IV-defined traumatic event will not develop PTSD (see

Breslau, 1998), and many individuals displaying the PTSD symptom pattern may not have experienced a related traumatic event.

Limitations of this study include the small sample sizes and use of mainly self-reports,

which might have influenced the results if people misunderstand certain items. Future

research could take several directions. First, the data raise doubts about the assessment

of PTSD by self-report measures: these may identify many PTSD patients as well as

anxiety patients without PTSD. However, some self-report instruments might work

better than others, such as inventories that measure many different conditions together

(i.e. multiscale tests), which is an empirical issue that awaits future research. Second, knowledge is scant with respect to the qualitative nature of reactions to traumatic and

common stressors. The nature of the stressor might determine different subtypes of

PTSD (e.g. depressive or physiologically responsive subtypes). Third, it might be

454 Iris M. Engelhard et al.

interesting to test whether treatment proven useful to PTSD is also effective for

individuals suffering from similar symptoms after stressors not defined as traumatic by

the DSM-IV. In sum then, the impact of traumatic events on mental health is often

determined by merely examining whether or not participants meet symptom criteria for

PTSD on a questionnaire. Our findings suggest that many people screened positive for

PTSD this way may not be actually suffering from the disorder.

Acknowledgements

This study was supported by an Innovational Research Incentive VENI Scheme (016.045.106) by

The Netherlands Organization for Scientific Research (NWO) awarded to Iris M. Engelhard. We

thank two anonymous reviewers for their helpful comments.

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Received 19 September 2006; revised version received 1 March 2007

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