LRSC

The impact of different diagnostic criteria on PTSD prevalence A comparison of PTSD prevalence using the DSM-IV and ICD-10 PTSD-criteria on a population of 242 Danish social work students MAJA O’CONNOR Department of Psychology MATHIAS LASGAARD University of Aarhus HELLE SPINDLER ASK ELKLIT The diagnostic criteria for PTSD have undergone several changes in the last two decades. This may in part explain the great variance in PTSD prevalence found in existing research. The objective of this study is to investigate the influence of different diagnostic criteria and different combinations of criteria on PTSD prevalence. A sample of 242 Danish social work students (M =29.2 years) completed a list of potentially traumatizing events, major life events and the Harvard Trauma Questionnaire. A considerable difference in PTSD prevalence as a result of different diagnostic criteria of PTSD was found. Future meta-analyses and reviews of PTSD prevalence must take into account the impact of changing criteria on prevalence. Clinicians also need to address this issue when assessing PTSD.

Key words: Traumatic events, diagnostic criteria of PTSD, PTSD prevalence, DSM-IV, ICD-10.

Correspondence: Maja O’Connor, Department of Psychology, University of Aarhus, Jens Chr.

Skous Vej 4, 8000 Aarhus C, Denmark. Tel.: +45 8942 4926, Fax: +45 8942 4901. E-mail:

[email protected] The experience of a traumatic event involving actual or threatened death, or serious injury may lead to the development of PTSD. In turn, receiving a PTSD diagnosis may provide a client with the option of psychological or medical care, and compensation. However, the same person may be diagnosed differently depending on which general diagnostic criteria of PTSD is used and which specific criteria, from for example DSM-IV, has been selected. Clinicians and researchers studying psychological trauma need to be aware of the potential vari- ance in diagnostic outcome as a product of the diagnostic criteria used.

Prevalence of PTSD Many studies have aimed to establish the prevalence and risk of PTSD for specific traumatic events, e.g. violence (e.g. Boney-Mccoy & Finkelhor, 1995; ARTICLE Nordic Psychology, 2007, 59 (4) 317-331 This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 318 Maja O'Connor et al. NP, 2007 (3) Seedat, Nyamai, Njenga, Vythilingum & Stein, 2004), childhood abuse (Libby, Orton, Novis, Beals & Manson, 2005) and war (Khamis, 2005). In contrast, studies investigating a broad range of traumatic events and the associated risk of PTSD are not very common. Four national probability samples (Kessler, Sonnega, Bromet, Hughes & Nelson, 1995; Kessler, Berglund, Demler, Jin, Marikangas, et al., 2005; Perkonigg, Kessler, Storz & Wittchen, 2000; Frans, Rimö, Åberg & Fredrikson, 2005) and two epidemiological studies (Bernat, Ronfeldt, Calhoun & Arias. 1998; Hepp, Gamma, Milos, Ajdacic-Gross, et al., 2006) have explored a broad range of traumatic events in adult populations (based on a September 2006 PsycInfo search using different combinations of search keywords such as; PTSD, prevalence, ICD 10, DSM IV, epidemiologic study, probability study). Similarly, one national probability study (Elklit, 2002) and one epidemiological study (Costello, Erkanli, Fairbank & Angold, 2002) have explored the prevalence of traumatic events in adolescent populations (based on same search as above). These studies show that the majority of the adults and adolescents sampled had been exposed to one or more traumatic events, resulting in a considerable number of PTSD cases.

The rates of prevalence found in the above studies show great variation regard- less of age. The number of participants reporting one or more events ranges from 21 % to 87 % and there is large variation in the prevalence reported for specific events and most common event experienced. Moreover, the prevalence of PTSD shows great variation across studies. The lifetime risk of PTSD ranges from 0 % to 9 %, and varies markedly across different types of trauma, although most studies find sexual abuse/rape to be associated with an increased risk of PTSD. In line with the recent findings of Foa & Tolin (2006) most studies show that females are more likely to suffer from PTSD, despite males reporting more exposure to traumatic events than females.

The reported differences in event-rates and PTSD prevalence may be related to methodological differences, e.g. the degree of specificity of the measured events, the number of events investigated, differences in data collection methods, demographics, and cultural and community related variables. Furthermore, dif- ferent problems such as the effect of the inclusion of the emotional impact, the A2 criterion (a subjective component of PTSD involving a response of intense fear, helplessness, or horror) or the diagnostic boundaries of PTSD in DSM IV are associated with the use of the PTSD diagnosis and have been widely discussed (e.g. Norman, Stein & Davidson, 2007; Brewin, 2005; Creamer, McFarlane & Burgess, 2005; Schützwohl & Maercker, 1999; O’Donohue & Elliot, 1992).

This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 319 The impact of different diagnostic criteria on PTSD prevalence NP, 2007 (3) Development of the diagnostic criteria of PTSD The diagnostic criteria of PTSD have developed over time. Prior to the intro- duction of the PTSD diagnosis in DSM-III (APA, 1980), trauma-related symp- tomatology was recognized in DSM-I (1952) as Gross Stress Reaction, and in DSM-II as Adjustment Reaction of Adult Life (Wilson, 1994). In DSM-III different syndromes caused by various traumatic events were finally combined into one diagnosis, Post Traumatic Stress Disorder. To qualify for the diagnosis of PTSD the existence of a stressor “that would evoke significant symptoms of distress in almost anyone had to be identifiable” (criteria 1). The remaining criteria were grouped into three symptom sections consisting of: 2) re-experiencing the traumatic event (recurrent and intrusive recollections of the event, recurrent dreams, and/or feeling as if the traumatic event is re-occurring), 3) numbing or detachment (diminishes interest in significant activities, feeling detachment or estrangement from others, and/or constricted affect) and 4) symptoms not pres- ent before the traumatic event (hyper alertness or exaggerated startle response, sleep disturbance, survivor guilt, memory impairment or trouble concentrating, avoidance of activities that arouse recollection of the traumatic event, and/or intensification of symptoms when reminded of the traumatic event). At least one symptom from section 2 and 3 and at least two symptoms from section 4 must be present to qualify for the PTSD diagnosis.

The diagnostic criteria were thoroughly revised in DSM-III-R (APA, 1987) adding a new component (E) of duration of symptom clusters B, C, and D, for at least one month and with onset in the immediate aftermath of the traumatic event (B, C, and D were a revision of section 2, 3, and 4 in DSM-III). Furthermore now, the stressor criterion (A) stated that the person must have experienced “an event outside the range of usual human experience that would be markedly distressing to almost anyone”. The symptom clusters in DSM-III-R consisted of:

(B) persistent re-experiencing the traumatic event (recurrent and intrusive distress- ing recollections of the event, recurrent distressing dreams of the event, sudden acting or feeling as if the traumatic event is reoccurring and/or intense psycho- logical distress when exposed to situations reminding of the traumatic event):

(C) persistent avoidance or numbing in relation to the traumatic event (efforts to avoid thoughts or feelings associated with the trauma, efforts to avoid activities or situations evoking recollection of the trauma, inability to recall an important aspect of the trauma, markedly diminished interest in significant activities, feeling detachment or estrangement from others, restricted affect and or a sense of fore- shortened future), (D) persistent arousal not present before the trauma (difficulties falling or staying asleep, irritability or outbursts of anger, problems concentrating, hypervigilance, exaggerated startle response and/or physiologic reactivity when This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 320 Maja O'Connor et al. NP, 2007 (3) exposed to trauma related events). At least one symptom from cluster B, at least three symptoms from cluster C, and at least two symptoms from cluster D must be present to qualify for diagnosis (APA, 1987).

DSM-IV (APA, 1994) enlarged the definition of stressors into two subcriteria (A1 and A2) and a functional criterion of clinically significant distress or impairment (F). Relatively little research on criterion (F) has yet been published. According to DSM-IV (APA, 1994) the diagnosis of PTSD requires the exposure to a traumatic event that involves: (A1) Actual or threat of death or serious injury, or a threat to the physical integrity of self or others, and (A2) involving a response of intense fear, helplessness, or horror. Moreover, the diagnosis requires (B) persistent re- experiencing of the traumatic event, (C) persistent avoidance of stimuli associated with the trauma and numbing of general responsiveness, and (D) persistent symp- toms of increased arousal. Finally, (E) the full symptoms must be present for more than 1 month, and (F) the disturbance must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning. At least one symptom from cluster B, at least three symptoms from cluster C, and at least two symptoms from cluster D must be present to qualify for diagnosis.

In the International Classification of Diseases 9 (ICD-9) from 1978, the World Health Organization (WHO) recognized the possible emotional problems follow- ing traumatic experiences by including two diagnoses (Acute Reaction to Stress and Adjustment Reaction) (Joseph, Williams & Yule, 1997).

The WHO (1993) included a diagnosis of PTSD in their most recent edition, ICD-10, as “a reaction to severe stress and adjustment disorders”. To diagnose the disorder, identification of (A) a stressor that is “likely to cause severe distress in almost anyone” is necessary (e.g. disaster, combat, rape, terrorism, violent death of others). In addition the following symptoms are required: (B) repetitive symp- toms of re-experiencing the traumatic experience (intrusive recollection or re- enactment in memories, dreams, or imagery) or severe discomfort when reminded of the traumatic experience, (C) actual or preferred avoidance of reminders of the traumatic experience, (D) either (D1) partially or complete inability to recall important aspects of the traumatic event or (D2) two of the following symptoms of increased arousal (difficulty in falling or staying asleep, irritability or outbursts of anger, difficulty concentrating, hypervigilance, exaggerated startle response), and (E) the criteria B, C, and D must be met within 6 months of the traumatic event. Several studies and reviews have discussed differences and similarities between the general diagnostic criteria of PTSD in DSM-IV and ICD-10. Empirical stud- ies almost exclusively apply DSM-IV criteria in their research. In contrast, clinical diagnosis and practice in many countries is based on ICD-10. However, when applying evidence-based treatment of PTSD, this evidence almost exclu- sively builds on research using DSM-IV criteria for the diagnosis in question. This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 321 The impact of different diagnostic criteria on PTSD prevalence NP, 2007 (3) Consequently, there is a risk that using treatment strategies based on DSM-IV results in lack of coherence between evidence-based clinical practice and ICD-10 diagnosis.

General consensus holds that there are great similarities, but also important differences between the two systems, mainly that ICD-10 does not emphasize avoidance and increased arousal to the same extent as DSM-IV, and that DSM-IV includes criteria of more than 1 months duration (E) and impairment of function (F) that ICD-10 does not (Joseph et al., 1997; Peters, Slade, and Andrew, 1999; Andrews, Slade, and Peters, 1999; Lundin & Lofti, 1996; Lopez-Ibor, 2002; Peters, Issakidis, Slade & Andrews, 2005). It is noteworthy that only two studies investi- gating differences in identification of PTSD cases using DSM-IV and ICD-10 have been identified. These studies found that only 37% of cases identified through ICD-10 (PTSD prevalence = 7%) also fulfilled the criteria of DSM-IV (PTSD preva- lence = 3 %), while on the other hand 85% of cases fulfilling DSM-IV criteria also fulfilled ICD-10 criteria (Andrews et al., 1999; Peters et al., 1999). Peters and colleagues suggested that this difference appears because DSM-IV requires fulfillment of a functional criterion (F), and put more emphasis on symptoms of avoidance or numbing (C) compared to ICD-10 (Peters et al., 1999). Moreover, a study focusing on gender differences found twice as many cases of PTSD using ICD-10 compared to DSM-IV (Peters et al., 2005).

Diagnostic criteria and prevalence of PTSD Epidemiological studies have used different diagnostic criteria that likely influ- ence the reported prevalence of PTSD and hence possibly explain some of the differences (see Table 1). The results of a cohort study (n=367) by Hepp and colleagues (2006) in which they found no cases at all of full PTSD is worth mentioning. The participants in this study reported whether or not they, dur- ing the last 12 months, had experienced or witnessed an event that involved actual or threatened death, serious injury or threat to the physical integrity of others - corresponding closely to the DSM-IV criteria A1. Participants were only asked to categorize the type of event if they answered affirmative to this question. The estimated prevalence of lifetime exposure to potentially traumatic events was 28 %, which may be explained by the very broad formulation of this question in terms not easily understandable to the population investigated.

Another explanation could be that specific categories of events, as for example the categorizations developed by Kessler et al. (1995) are more likely to trigger recognition of specific, potentially traumatic events than the broader approach used by Hepp and colleagues (2006). This does not, however, explain why none of the 128 individuals fulfilling criteria A1 met all the remaining criteria This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 322 Maja O'Connor et al. NP, 2007 (3) of PTSD (Hepp et al., 2006). One reason may be that the participants, con- sistent with, for example, Perkonigg and colleagues (2000), had to meet all 6 specific diagnostic criteria (A-F) to qualify for the diagnosis of PTSD. However, in a Swedish probability study (n=1824) Frans and colleagues (2005) found a lifetime prevalence of 5.6 % using all 6 specific criteria of PTSD and using yes/ no answers to identify symptoms, hence possibly increasing the effect.

In comparison, the remaining studies described in Table 1 found a lifetime prevalence of PTSD ranging from 4-9 %. This may be explained by the use of less specific DSM-IV criteria for PTSD or different general diagnostic criteria (DSM-III-R).

Table 1 Lifetime prevalence of PTSD and general and specific criteria in national populations Lifetime prevalence (All partici- pants)Prevalence in exposed participants (one or more potentially traumatic events reported)General and specific diagnostic criteria applied Kessler et al., 19957.8 % 11.8 % DSM-III-Ra Kessler et al., 20056.8 % - DSM-IVa Elklit, 20029 % 10.3% DSM-IV A1, B, C, & D Bernat et al.

19984 % 12 % DSM-IV A1, A2, B, C, & D Hepp et al.

20060 % 0 % DSM-IV A1, A2, B, C, D, E, & F Perkonigg et al., 20001.3 % 7.8 % DSM-IV A1, A2, B, C, D, E, & F Frans et al., 20055.6 % 6.9 % DSM-IV A1, A2, B, C, D, E, & F a No information available about specific criteria used.

While trauma and PTSD in non-clinical adult populations have been investigated (e.g. Kessler et al., 1995; Kessler et al 2005; Perkonigg et al., 2000; Frans et al., 2005), few studies have investigated the effect of different diagnostic criteria applied to the same population. Three studies have found significant variations in PTSD prevalence according to the different diagnostic criteria (Bernat et al. 1998; Peters et al., 2005; Peters et al., 1999). Concurrently, the prevalence of PTSD varies widely between studies. Different diagnostic criteria and configurations of symptoms may partly explain variations found in studies of PTSD prevalence, This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 323 The impact of different diagnostic criteria on PTSD prevalence NP, 2007 (3) both in non-clinical and clinical populations, emphasizing the relevance of studying this issue further.

Aim of the study The aim of the present study was to explore the impact of different diagnostic criteria on PTSD prevalence in an adult non-clinical population. The hypotheses investigated are: 1) The diagnostic tool used influences the PTSD prevalence, 2) Introducing additional specific DSM-IV criteria for PTSD reduces the prevalence rate of PTSD.

Material and methods Participants The sample for the current study consisted of 242 adult students with a mean age of 33 years (SD = 11.26; range 16-61 years). There were 209 (86 %) females and 33 (14 %) males. Forty two percent of the students lived alone (unmarried, divorced or widowed), while 56 % lived together with a partner (married or cohabiting). 50 % of the students had children. The average length of education was 13 years (SD 3.1; range 7-24 years).

Procedures The first author introduced the study to the students and was available for clarifying questions while the participants completed the questionnaire in the classroom. Participation was voluntary and the response rate was 99%. The par- ticipants were recruited from three different schools of intermediate educational level located in Aarhus, Denmark. The participants were selected because of their status as adult social worker students, of which the majority had a non- university background. A Tukey B post hoc analysis, that allow statistically reli- able identification of differences between two groups or more (Pallant, 2005), showed few differences between the three groups on parameters of gender, age and range of traumatic events and life events.

Measures The first part of the questionnaire contained socio-demographic questions about gender, age, education and family conditions. Following that, two types of stressors, traumatic experiences ad modum Kessler and colleagues (1995) and distressing life events were investigated. Distressing life-events were reported by answering the following question: “Within the last year have you experienced This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 324 Maja O'Connor et al. NP, 2007 (3) major life-events/changes?”. Subsequently, the students were asked about the experience of different traumatic events (see Table 2).

Table 2 Trauma and Life Events According to Exposure and Prevalence of PTSD (fulfilling criteria A1, B, C, and D of DSM-IV) EventFrequency (%)Choice of most distressing event (%)Relative risk (%) PTSDSub clinical PTSD Traumatic events Accident 20 38 38 32 Shock by some one close being exposed to a traumatic event 16 21 51 35 Threat of violence 15 18 38 34 Serious illness 13 28 50 23 Childhood abuse 14 52 75 14 Violent assault 10 24 41 28 Witness other people getting injured or killed 9 3 38 29 Rape 2 86 100 0 Recent life events Move of residence 17 13 54 20 Divorce/break up with a partner 6206414 Change of employment or education 5 6 46 8 Getting fireda 238-- a = less than 5 cases Harvard Trauma Questionnaire-Part IV (Mollica, Capsi-Yavin, Bollini, & Truong, 1992) was used to estimate the occurrence of PTSD. HTQ consists of 30 items, rated on a 4-point Likert scale (1 = not at all; 4 = very often). Sixteen items relate to the three core clusters in PTSD in DSM-III-R: intrusion, avoidance, and arousal.

In the present study, participants rated the HTQ on the basis of the most stressful life or traumatic event experienced. Participants answered HTQ in relation to their reaction in the time immediately after the stressful event. Only scale items ≥ 3 on HTQ were considered for a PTSD diagnosis. Recognition of a sub clinical level of PTSD was given if the respondent met two of the three criteria.

The Danish version of the HTQ has been found to be a reliable and valid mea- sure (Bach, 2003). Moreover, HTQ ratings according to the DSM-III-R diagnostic This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 325 The impact of different diagnostic criteria on PTSD prevalence NP, 2007 (3) criteria of PTSD showed an 88% concordance with interview based estimates of PTSD (Mollica et al., 1992). The internal consistency of the PTSD scale and subscales in the present study was good for the HTQ (Total score: α = .95; intru- sion: α = .81; avoidance: α = .73; arousal: α = .73).

Furthermore, the following four single questions relating to the chosen event were included in the study with the purpose of establishing whether the stressful event selected when filling in the HTQ met the A1 and A2 criteria included in DSM-IV-TR. 1) Were you in mortal danger while it happened? 2) Were others in mortal danger? 3) Were you injured? 4) Did you feel helpless or horrified?

Moreover, the participants were asked to report how much each symptom dis- turbed her/him during the last month to investigate present PTSD symptoms.

Statistical Analysis The sample used in this study was extracted from a larger study. Prior to data analysis, we excluded a fourth group, consisting of 86 predominantly young, male, trainee-craftsmen, due to inadequate data quality.

To fulfill the criteria of DSM-III, the following demands had to be met: (1) The participant reported one or more traumatic events; the participant reported ≥ 3 on: (2) one or more intrusion items (HTQ 1-3), (3) on one or more numbing items (HTQ 4, 5, 13) and (4) on two or more items of symptoms not present before the traumatic event (HTQ 6-8, 11, 12, 16, 20).

To fulfill the five criteria of DSM-III-R, the following was computed: (A) The participant reported one or more traumatic events; the participant reported ≥ 3 on: (B) one or more intrusion items (HTQ 1-3), (C) three or more symptoms of persistent avoidance or numbing (HTQ 4, 5, 11-15), (D) two or more symptoms of persistent arousal not present before the trauma (HTQ 6-10, 16). To fulfill the DSM-IV criteria of PTSD the participant reported (A1) one or more traumatic events and (A2) a sense of helplessness or horror in relation to the traumatic event. The participant reported one or more traumatic events; the participant reported ≥ 3 on (B) one or more intrusion items (HTQ 1-3, 16) item 16 containing both the physiological and psychological stress of being reminded of the event; (C) three or more symptoms of persistent avoidance or numbing (HTQ 4, 5, 11-15) and (D) two or more symptoms of persistent arousal not pres- ent before the trauma (HTQ 6-10). HTQ18 “Difficulties with carrying out work or daily functions” was defined as the DSM-IV criterion (F) where the disturbance must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning. Criterion (F) was defined as fulfilled if the participant reported a score ≥ 3 on this item. This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 326 Maja O'Connor et al. NP, 2007 (3) To fulfill the four first criteria of ICD-10 PTSD, the following algorithm was applied: (A) The participant reported one or more traumatic events; the par- ticipant reported ≥ 3 on (B) one or more symptoms of persisting intrusion or re-experiencing the traumatic event (HTQ 1-3 or 16); (C) actual or preferred avoidance of circumstances associated with the stressor (HTQ 11 or 15); (D) inability to recall important aspects of the trauma (HTQ 12) or two out of five symptoms of increased arousal (HTQ 6-10). The last criteria (E) where B, C, and D must be met within 6 months of the traumatic event could not be included in the computation.

Frequency analysis or Chi-square analyses were computed of the concordance between participants identified as fulfilling the diagnostic criteria of PTSD in ICD-10 compared to DSM-IV and DSM-IV compared to ICD-10. Only par- ticipants with valid scores on both parameters were included. All analyses were carried out using SPSS, version 13.

Results A total of 87 % of the students reported at least one life event or at least one traumatic experience (see Table 2). Eighty percent of the students reported one or more traumatic event (one event = 31 %, two events = 23 %, three or more events = 26 %). The average number of experienced traumatic events was 1.7 (SD = 1.5), and the most common events reported were bereavement, shock by someone close being exposed to a traumatic event, threat of violence, and accident. Twenty-nine percent of the students reported one or more distressing life events within the last year (one event = 23 %, two events = 6 %, three or more events = 1 %). The average number of distressing life events per student was 0.4 (SD = 0.6), and the most commonly reported life event was change of residence, and divorce/separation.

The PTSD prevalence was remarkably high in those reporting certain major life-events within the last year. Divorce or break-up with a partner was the highest ranking (64% with PTSD), followed by change of residence (54%), and change of employment or education (46%). The average number of experienced events was higher among participants with PTSD than exposed participants without PTSD (2.6 vs. 1.9 events).

Table 3 illustrates that the diagnostic tool used influenced the PTSD prevalence rate. The largest difference was found between ICD-10 with a PTSD prevalence of 35% and DSM-IV including criteria A1, A2, B, C, D, E, and F with a PTSD prevalence of 11%. Furthermore, as expected, introducing additional DSM-IV criteria reduced the PTSD prevalence. This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 327 The impact of different diagnostic criteria on PTSD prevalence NP, 2007 (3) Table 3 Prevalence of lifetime PTSD according to different diagnostic criteria and different con- figurations of specific criteria within DSM-IV PTSD-prevalenceSub-clinical PTSD (2 out of 3 criteria: B, C, and D) ICD-10 A, B, C, & D35 % (n=84) 17 % (n=42) DSM-III-R A, B, C, & D30 % (n=73) 16 % (n=39) DSM-III 1, 2, 3 & 429 % (n=70) 14 % (n= 33) DSM-IV B, C, D, & E25 % (n=61) 17 % (n=42) DSM-IV A1, B, C, D, & E22 % (n=54) 16 % (n=39) DSM-IV A2, B, C, D, & E20 % (n=48) 15 % (n=35) DSM-IV A1, A2, B, C, D, & E17 % (n=42) 14 % (n=33) DSM-IV A1, A2, B, C, D, E, & F11 % (n=26) 4 % (n=10) Using all 6 DSM-IV criteria of PTSD, 26 participants qualified for the full PTSD diagnosis. Ninety two percent of these (24 participants) also qualified for the ICD-10 diagnosis of PTSD using criteria A, B, C, and D. Eighty one participants qualified for the ICD-10 diagnosis of PTSD. Three participants were excluded because of missing scores in the DSM criteria. Out of the 81 participants, only 30 percent (24 participants) qualified for the full diagnosis of PTSD according to DSM-IV (criteria A1, A2 B, C, D, E, and F).

Discussion In line with findings from other studies (e.g. Bernat et al., 1998) a high num- ber (80%) of participants in the present study reported at least one potentially traumatic event. PTSD prevalence was found to vary considerably according to which diagnostic tool was used. The PTSD prevalence according to ICD-10 was 35% while according to DSM-IV using similar specific criteria (A1, B, C, D, and E) the PTSD prevalence was 22% (see Table 3). The results indicate that within the same population the diagnostic tool chosen may have a strong impact on the number of cases of PTSD identified. This may explain why the concor- dance between PTSD in DSM-IV versus ICD-10 was only 30%. In addition, This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 328 Maja O'Connor et al. NP, 2007 (3) a lack of congruency between practice and research poses a serious problem in countries that use the ICD-10 in clinical work as the empirical evidence is based DSM PTSD. Such in-congruency may result in PTSD losing its credibility as a meaningful and applicable diagnosis in clinical work in countries using ICD-10. In line with the findings by Peters et al. (2005) the present study found a much lower concordance between PTSD in ICD-10 compared to DSM-IV (30 % concordance) and PTSD in DSM-IV compared to ICD-10 (91% concordance).

The DSM-IV PTSD prevalence was reduced as additional specific diagnostic criteria were added. This result may seem common sense, but the fact is that several studies only specify the general diagnostic criteria used (e.g. ICD-10 or DSM-IV) without specifying exactly how they operationalized these criteria. As mentioned, large variation has been found in PTSD prevalence as defined by DSM-IV criteria both in clinical and non-clinical samples. One of the reasons for this variability may be the fact that different specific criteria have been applied, but have not been clearly operationalized when reporting the results. This poses an obstacle when reviewing PTSD prevalence. According to the results of this study, it is necessary to take both the general and specific DSM criteria applied into consideration before comparing results from different studies.

The main problem is that the applied specific DSM-IV criteria, apart from A1 and A2, are rarely operationalized in studies of PTSD prevalence. Another is that the significant changes in all general DSM criteria variables from 1980 to 1994 must be taken into consideration when comparing results from studies using different general criteria. Obviously, this makes reviewing the literature difficult.

To avoid the risk of drawing conclusions based upon incomplete information, future review work on estimation of PTSD prevalence needs to take the variance in PTSD prevalence produced by unspecified and varying diagnostic criteria into account. Also existing meta-analyses and reviews should be assessed with this in mind (e.g. Tolin & Foa, 2006). In conclusion, when investigating PTSD prevalence it is crucial that researchers pay careful attention to the applied diagnostic criteria when performing reviews and meta-analysis. Furthermore researchers must be urged to specify the precise PTSD-criteria used when reporting studies involving PTSD prevalence.

The high PTSD prevalence in the present study (see Table 2) might be explained by the fact that many of the participants recently left home or got divorced, moved into their first own residence and started their further education in a new field.

This type of event may cause stress, but should not lead to PTSD, as the DSM-IV criteria A1 is not fulfilled. Even so, in a Dutch population including 832 adults, Mol, Arntz, Metsemakers, Dinant, Vilters-Van, et al. (2005) found that PTSD scores were higher after life events than after traumatic events from the past 30 years. In line with this, other studies have reported significant associations This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 329 The impact of different diagnostic criteria on PTSD prevalence NP, 2007 (3) between PTSD symptoms and 1) the exposure of farmers to an epidemic of foot and mouth disease causing a mass cull of livestock (Olff, Koeter, Van Haaften, Kersten, & Gersons, 2005), 2) extreme pressure including public humiliation in the work setting (Ravin & Boal, 1989), 3) victims of bullying at work (Mikkelsen & Einarsen, 2002), and 4) parental divorce/an absent parent (Elklit, 2002; Joseph, Mynard & Mayall, 2000). In sum, several studies have reported PTSD symptoma- tology in cases lacking a DSM-IV adequate A1 stressor.

One possible reason for these findings may be that some stressors, not including actual or threat of death or serious injury, or a threat to the physical integrity of self or others, pose a threat to identity (Brewin, 2003; Mol et al. 2005). A threat to the psychological or social integrity of a person is in some cases comparable to the threat of the physical integrity, included in the present diagnostic criteria.

Another potential explanatory factor could be that accumulation of traumatic events experienced was related to PTSD prevalence, since the average number of experienced events was higher among participants with PTSD than among exposed participants without PTSD. In a nationally representative sample of Danish adolescents (Shevlin & Elklit, in press) latent class analysis was used to identify clusters or latent classes of events. In addition, the relationships between the latent classes and living arrangements and diagnosis of post-traumatic stress disorder (PTSD) were estimated. A three-class solution was found to be the best description of multiple adverse life events, and the three classes were labelled ‘Low Risk’, ‘Intermediate Risk’, and ‘High Risk’. The High Risk group were found to have a relatively high likelihood of experiencing multiple traumas and were 13 times more likely to have a PTSD diagnosis.

The results of the current study should be interpreted with caution. Firstly, the study is cross-sectional and retrospective. Secondly, the high PTSD prevalence found could be an indication of the fact that our sample was non-representative.

On the other hand, the sample of social work students represents a group that may be more similar to the general population than undergraduate university students.

Our results cannot be generalized to other populations. Despite the limitations, the study explores an understudied issue in the field of traumatic stress.

To summarize, the results from this study indicate that extreme care should be taken regarding both the general and specific diagnostic criteria used when assessing PTSD prevalence. Often only the general criteria (ICD-10 or DSM-IV) and the A1 and A2 criteria of DSM-IV are operationalized, making meta-analysis and reviews on PTSD prevalence difficult to perform in a satisfactory manner.

When reporting future research on PTSD prevalence a precise description of which specific DSM-IV criteria are used and operationalized is required. In time, this could lead to consensus on the use and operationalization of PTSD criteria in empirical work and clinical practice. In addition, future studies should also con- This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 330 Maja O'Connor et al. NP, 2007 (3) sider the possibility of alternative structures of PTSD symptomatology including a widening of the criteria to encompass situations that might threaten the current life conditions and psychological integrity of the person (see Brewin, 2003).

REFERENCES APA (1980). Diagnostic and statistical manual of mental disorders. Third Edition. Washington, DC: American Psychiatric Association.

APA (1987). Diagnostic and statistical manual of mental disorders. Third edition, revised.

Washington, DC: American Psychiatric Association APA (1994). Diagnostic and statistical manual of mental disorders. Fourth edition. Washington, DC: American Psychiatric Association Andrews, G., Slade, T., & Peters, L. (1999). Classification in psychiatry: ICD-10 versus DSM-IV.

British Journal of Psychiatry, 174, 3-5.

Bach, M.E., (2003). En empirisk belysning og analyse af „Emotional Numbing“ som en eventuel selvstændig faktor i PTSD. Psykologisk Studieskriftserie 6(1), 1-200.

Bernat, J., Ronfeldt, H. M., Calhoun, K. S., & Arias, I. (1998). Prevalence of traumatic events and peritraumatic predictors of posttraumatic stress symptoms in a nonclinical sample of college students. Journal of Traumatic Stress, 11(4), 645-664.

Brewin, C. (2005). Systematic review of screening instruments for adults at risk of PTSD. Journal of Traumatic Stress, 18(1), 53-62.

Costello, E. J., Erkanli, A., Fairbank, J. A., & Angold, A. (2002). The prevalence of potentially trau- matic events in childhood and adolescence. Journal of Traumatic Stress, 15(2), 99-112.

Cramer, M., McFarlane, A. & Burgess, P. (2005). Psychopatology following a trauma: The role of subjective experience. Journal of Affective Disorders, 86, 175-182.

Elklit, A. (2002). Victimization and PTSD in a Danish national youth probability sample. Journal of the American Academy of Child & Adolescent Psychiatry, 41(2), 174-181.

Frans, Ö., Rimmö, P.-A., Åberg, L., & Fredrikson, M. (2005). Trauma exposure and post-traumatic stress disorder in the general population. Acta Psychiatrica Scandinavica, 111(4), 291-299.

Hepp, U., Gamma, A., Milos, G., Eich, D., Ajdacic-Gross, V., Rössler, W., Angst, J., Schnyder, U.

(2006). Prevalence of exposure to potentially traumatic events and PTSD: The Zurich Cohort Study. European Archives of Psychiatry and Clinical Neuroscience, 256(3), 151-158.

Joseph, S., Williams, R., & Yule, W. (1997). Understanding post-traumatic stress. A psychosocial perspective on PTSD and treatment. UK: Wiley.

Joseph, S., Mynard, H. & Mayall, M. (2000). Life-Events and Post-traumatic Stress in a Sample of English Adolescents. Journal of Community & Applied Social Psychology, 10, 475-482.

Kessler, R. C., Berglund, P., Demler, O., Jin, R., Merikangas, K. R., & Walters, E. E. (2005). Lifetime prevalence and age-of-onset distributions of DSM-IV disorders in the national comorbidity survey replication. Archives of General Psychiatry, 62(6), 593-602.

Kessler, R. C., Chiu, W.T., Demler, O., & Walters, E. (2005). Prevalence, severity, and comorbid- ity of 12-month DSM-IV disorders in the national comorbidity survey replication. Archives of General Psychiatry, 62(6), 617-627.

Kessler, R. C., Sonnega, A., Bromet, E., Hughes, M., & Nelson, C. B. (1995). Posttraumatic stress disorder in the National Comorbidity Survey. Archives of General Psychiatry, 52(12), 1048-1060.

Khamis, V. (2005). Post-traumatic stress disorder among school age Palestinian children. Child Abuse & Neglect, 29, 81-95.

Libby, A., Orton, H., Novis, D., Beals, J. & Manson, S. (2005). Childhood physical and sexual abuse and subsequent depressive and anxiety disorders for two American Indian tribes.

Psychological Medicine 35(3), 329-340.

López-Ibor, J. J. (2002). The classification of stress-related disorders in ICD-10 and DSM-IV.

Psychopathology, 35, 107-111.

This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly. 331 The impact of different diagnostic criteria on PTSD prevalence NP, 2007 (3) Lundin, T., & Lotfi, M. (1996). Posttraumatic stress disorder in DSM-III-R, DSM-IV, and ICD-10: A comparison and evaluation of the significance of the respective diagnostic criteria. Northern Journal of Psychiatry, 50, 11-15.

Mikkelsen, E. & Einarson, S. (2002), Basic assumptions and symptoms of post-traumatic stress among victims of bullying at work, European Journal of Work and Organizational Psychology, 11(1), 87-111.

Mol, S. S. L., Arntz, A., Metsemakers, J. F. M., Dinant, G.-J., Vilters-Van Montfort, P. A. P., & Knottnerus, J. A. (2005). Symptoms of post-traumatic stress disorder after non-traumatic events:

Evidence from an open population study. British Journal of Psychiatry, 186(6), 494-499.

Norman, S., Stein, M. & Davidson, J. (2007). Profiling Posttraumatic Functional Impairment. The Journal of nervous and Mental Disease, 195(1), 48-53.

Mollica, R., Caspi-Yavin, Y., Bollini, P., Truong, T., Tor, S. & Lavelle, J. (1992). The Harvard Trauma Questionnaire. Validating a Cross-Cultural Instrument for Measuring Torture, Trauma an Posttraumatic Stress Disorder in Indochinese Refugees. The Journal of Nervous and mental Disease, 180(2), 111-118.

O’Donohue, W., & Elliott, A. (1992). The current status of post-traumatic stress disorder as a diag- nostic category: Problems and proposals. Journal of Traumatic Stress, 5(3), 421-439.

Olff, M., Koeter, M., Van Haaften, E., Kersten, P. & Gersons, B. (2005). Impact of a foot and mouth disease crisis on post-traumatic stress symptoms in farmers. British Journal of psychiatry, 186, 165-166.

Pallant, J. (2005). SPSS Survival Manual. 2nd edition. A step by step guide to analysis using SPSS for Windows (Version 12). UK: Open University Press.

Perkonigg, A., Kessler, R. C., Storz, S., & Wittchen, H.-U. (2000). Traumatic events and post- traumatic stress disorder in the community: Prevalence, risk factors and comorbidity. Acta Psychiatrica Scandinavica, 101(1), 46-59.

Peters, L., Issakidis, C., Slade, T., & Andrews, G. (2005). Gender differences in the prevalence of DSM-IV and ICD-10 PTSD. Psychological Medicine, 35, 1-9.

Peters, L., Slade, T., & Andrews, G. (1999). A comparison of ICD10 and DSM-IV criteria for post- traumatic stress disorder. Journal of Traumatic Stress, 12(2), 335-343.

Ravin, J. & Boal, C. (1989). Post-Traumatic Stress Disorder in the Work Setting: Psychic Injury, Medical Diagnosis, Treatment and Litigation. American Journal of Forensic Psychiatry, 10(2), 5-23.

Schützwohl, M., & Maercker, A. (1999). Effects of varying diagnostic criteria for posttraumatic stress disorder are endorsing the concept of partial PTSD. Journal of Traumatic Stress, 12(1), 155-165.

Seedat, S., Nyamai, C., Njenga, F., Vythilingum, B. & Stein, D.J. (2004) Trauma exposure and post-traumatic stress symptoms in urban African schools. British Journal of Psychiatry, 184, 169-175.

Shevlin, M. & Elklit, A. (in press). A latent class analysis of adolescent adverse life events based on a Danish national youth probability sample. Journal of Nordic Psychiatry.

Tolin, D. F., & Foa, E. B. (2006). Sex differences in trauma and posttraumatic stress disorder: A quantitative review of 25 years of research. Psychological Bulletin, 132(6), 959-992.

Wilson, J. (1994). The historical evolution of PTSD diagnostic criteria: From Freud to DSM-IV.

Journal of Traumatic Stress, 7(4), 681-698.

World Health Organization (1993). ICD-10. The ICD-10 classification of mental and behavioural disorders. ISBN 92 4 154455 4.

This document is copyrighted by the American Psychological Association o\ r one of its allied publishers.

This article is intended solely for the personal use of the individual u\ ser and is not to be disseminated broadly.