Eric Vermetten, Anne Germain and Thomas C. Neylan (eds.)Sleep and Combat-Related Post Traumatic Stress Disorderhttps://doi.org/10.1007/978-1-4939-7148-0_14

14. Assessment of Posttraumatic Stress Disorder

Christy A. Blevins¹, Margaret T. Davis² and Frank W. Weathers³

(1)

Mental Health Division, VA Portland Health Care System, Portland, OR, USA

(2)

Departments of Psychiatry & Radiology and Biomedical Imaging, Yale University School of Medicine, New Haven, CT, USA

(3)

Department of Psychology, Auburn University, Auburn, AL, USA

Frank W. Weathers

Email: weathfw@auburn.edu

Keywords

Sleep assessmentPTSDSleep disturbancesScreening measures

Assessment of Posttraumatic Stress Disorder

Posttraumatic stress disorder (PTSD) is a chronic and debilitating mental disorder that represents a pathological outcome following exposure to catastrophic life events such as combat, physical or sexual assault, transportation accidents, and natural disasters. PTSD is a multifaceted syndrome comprising multiple related but distinct symptom clusters (reexperiencing the trauma, avoidance of trauma-related reminders, emotional numbing, hyperarousal) and often co-occurs with other mental disorders such as depression, anxiety disorders, and substance use disorders. PTSD also often co-occurs with sleep disorders such as insomnia and obstructive sleep apnea, which, in addition to arousal-related sleep disturbance included in the symptom criteria for PTSD, highlights the importance of assessing sleep among those with PTSD.

Originally classified as an anxiety disorder when it was introduced as a mental disorder in DSM-III in 1980, PTSD is now grouped in the trauma- and stressor-related disorders in DSM-5, along with other disorders with a stressful life event as a diagnostic criterion, including reactive attachment disorder, disinhibited social engagement disorder, acute stress disorder, and adjustment disorders. In addition to this reclassification, a number of substantive revisions to the PTSD diagnostic criteria were made for DSM-5. These include (a) a more specific explication of Criterion A and removing Criterion A2 requiring an emotional response to the trauma of fear, horror, or helplessness; (b) an increase from 17 to 20 symptom criteria, with three new symptoms and revision of several existing symptoms; (c) an increase from three to four symptom clusters, with the separation of avoidance symptoms from numbing symptoms and a reconceptualization of the numbing symptoms as negative alterations in cognitions and mood; and (d) the addition of a dissociative subtype. Further, diagnostic criteria for children 6 years old or younger are specified separately. Perhaps the most significant change to the PTSD criteria is the separation of avoidance and numbing, a decision made primarily on the basis of factor analytic evidence that these are distinct symptom clusters (e.g., [41]).

The complexity of the typical clinical presentation of PTSD poses significant challenges for psychological assessment. Fortunately, over the last 30 years, substantial progress has been made in the development and validation of a wide range of assessment measures for a variety of research and clinical applications. In this chapter we describe a number of the most widely used measures used in the assessment of PTSD, including interviews, self-report measures, brief screening measures, multiscale inventories, and measures of closely related symptoms such as dissociation, guilt, and sleep disturbance. Due to space limitations, we limit our review to PTSD measures for adults and do not cover assessment of trauma exposure, assessment of PTSD in children, or assessment of acute stress disorder or complex PTSD. Recent reviews on these topics may be found elsewhere (e.g., [8, 32]).

Given that DSM-5 was only recently released, many descriptions of the measures and the summaries of their supporting psychometric evidence are based on DSM-IV or earlier versions of the PTSD diagnostic criteria. Presumably most of the measures discussed will be updated for DSM-5, and the psychometric properties of the revised versions will be investigated. For those measures that have been revised for DSM-5, including the Clinician-Administered PTSD Scale (CAPS) and PTSD Checklist (PCL), we summarize the specific revisions and related psychometric evidence.

Review of Assessment Instruments

In this section we review the most widely used assessment instruments of PTSD symptomatology in traumatized adults. We begin with a review of structured interviews and self-report measures, which are further categorized based on whether or not they correspond directly with DSM diagnostic criteria. This is followed by a section on brief screening measures and multiscale inventories that include a PTSD scale. Last, we review assessment instruments for dissociation and posttraumatic guilt.

Although we do not discuss assessment of trauma exposure in detail, it is important to note at the outset the importance of establishing Criterion A in diagnosing PTSD. To meet full diagnostic criteria for PTSD, an individual must not only have all the requisite symptoms, but these symptoms must have developed in response to a stressful life event that satisfies the definition of a trauma as described in Criterion A. Although the definition of Criterion A has evolved since DSM-III (see [113], for a full discussion), the essence of a traumatic stressor is exposure to an event involving life threat or serious injury, through directly experiencing the event, witnessing it, or learning about it happening to a loved one. Some of the instruments described below include items assessing trauma exposure. Those that do not may be supplemented by administration of one of many available trauma exposure measures (for a review, see [42, 98, 107]). Some of the most widely used stand-alone trauma exposure measures include the Life Stressor Checklist – Revised (LSC-R; [127]), Trauma History Questionnaire (THQ; [60]), and Traumatic Life Events Questionnaire (TLEQ; [79]). Both the LSC-R and TLEQ include assessment of A2 (e.g., experience of fear, helplessness, or horror at the time of the event), while the THQ assesses only A1 (e.g., experienced an event involving actual or threatened death or serious injury). All three instruments assess for a wide variety of potentially traumatic events including natural disaster, combat, serious accident, life-threatening illness, and sexual and physical assault. Another trauma exposure measure, the Life Events Checklist for DSM-5 (LEC-5; [118]), was recently updated to reflect changes to Criterion A in DSM-5. The LEC was originally developed as the trauma assessment component of the Clinician-Administered PTSD Scale (discussed below). The revised version is available in two formats, standard and extended. The standard version is a checklist that assesses for different levels of exposure (e.g., experienced, witnessed, learned about) to 17 categories of potentially traumatic events. The extended version includes the standard version plus a series of questions designed to identify the worst event and determine whether it meets the definition of a trauma according to DSM-5 Criterion A.

Structured Interviews

Structured interviews are essential tools in the assessment and diagnosis of psychopathology. Because the prompts are standardized, structured interviews promote systematic and comprehensive coverage of all diagnostic criteria. Further, interviews provide clinicians the opportunity to clarify potentially confusing symptoms and other diagnostic criteria to ensure that respondents know what is being asked. Finally, and most importantly, interviews allow clinicians to use clinical judgment to evaluate the relevance and severity of respondents’ symptom reports. For these reasons, structured interviews are considered to be the gold standard for diagnosing mental disorders and are used as the criterion in evaluating the performance of self-report measures. In this section we briefly review five of the most widely used structured interviews for the assessment of PTSD.

Clinician-Administered PTSD Scale

Developed in 1989 at the National Center for PTSD, the Clinician-Administered PTSD Scale (CAPS; [12, 13]) is one of the most widely used and extensively validated structured interviews for PTSD. The CAPS assesses all DSM-IV PTSD criteria, including Criterion A, the 17 DSM-IV PTSD symptoms, and degree of functional impairment. In addition, the CAPS assesses associated symptoms of dissociation and guilt, response validity, overall symptom severity, and degree of improvement since a prior assessment. Further, for symptoms that are not inherently linked to the index traumatic event – including the emotional numbing, hyperarousal, and dissociative symptoms – the CAPS assesses the degree of trauma relatedness, using a specific prompt and three-point rating scale (definitely, probably, unlikely). The CAPS may be used to assess PTSD over the past month, the past week, or the worst month lifetime.

The CAPS provides standardized initial and follow-up prompts to assess the frequency and intensity of each symptom, which are rated on separate five-point (0–4) rating scales. Prompts and rating scales reference specific behavioral anchors to increase precision and enhance reliability. Frequency and intensity scores for each item may be summed to create a symptom severity score, and frequency, intensity, and severity scores may be summed across items to create composite scores for each symptom cluster and for the full PTSD syndrome.

A number of scoring rules have been developed and evaluated for converting CAPS symptom ratings into a dichotomous PTSD diagnosis [115]. The most commonly used rule is the F1/I2 rule, which involves considering items with a frequency rating of 1 or higher and an intensity score of 2 or higher as symptom endorsed, then following the DSM-IV diagnostic rule (1 reexperiencing symptom, 3 avoidance/numbing symptoms, and 2 hyperarousal symptoms). The CAPS has been extensively evaluated and has been shown to have excellent psychometric properties in a wide range of populations and settings [116].

The CAPS has been revised for DSM-5, and the resulting CAPS-5 [117] is currently undergoing psychometric evaluation. The goals for the revision were to (a) achieve concordance with DSM-5 PTSD criteria by adding items to assess new symptoms and revising existing items to accurately reflect modifications to existing symptoms and (b) streamline administration and scoring while (c) maintaining backward compatibility insofar as possible with the CAPS for DSM-IV. The CAPS-5 still provides standard initial and follow-up prompts to evaluate the frequency and intensity of symptoms, but prompts are presented in a more user-friendly format and sequence. Further, although interviewers still make interim ratings of frequency and intensity, they combine this information, using prespecified thresholds, to make a final rating of symptom severity on a single 0–4 scale. This approach, including the symptom-specific threshold values, is based on one of the previously developed rationally derived CAPS scoring rules, the Clinician-Rated 60 (CR60) rule.

PTSD Symptom Scale: Interview Version

The PTSD Symptom Scale – Interview Version (PSS-I; [51]) is a 17-item structured interview with each item corresponding to one of the 17 DSM-IV PTSD symptom criteria. Interviewers ask a brief initial prompt for each criterion and then rate severity over the past 2 weeks on a four-point scale (0 = not at all, 1 = once per week or less/a little, 2 = two to four times per week/somewhat, 3 = 5 or more times per week/very much). The original DSM-III-R version of the PSS-I included anchors describing only intensity (e.g., 1 = a little), which was later revised to include anchors describing both intensity and frequency, albeit on a single scale. The PSS-I yields symptom severity and diagnostic data. A total symptom severity score is obtained by summing ratings for all 17 items. A PTSD diagnosis is obtained by counting symptoms rated as one or greater as present and applying the DSM-IV diagnostic rule.

PSS-I scores have demonstrated strong psychometric properties. Foa et al. [51] found the PSS-I to have good reliability, as indicated by an alpha of 0.85 and mean item-scale total correlation of 0.45. Test-retest reliability for the total severity score also was high (0.80), as was the kappa coefficient for a PTSD diagnosis (0.91). Using the SCID-PTSD module as the criterion, the PSS-I demonstrated excellent diagnostic utility, with sensitivity of 0.94, specificity of 0.96, and efficiency of 0.94. Extending Foa et al.’s [51] initial psychometric study, Foa and Tolin [50] provided further evidence for the reliability, internal consistency, and convergent validity of the PSS-I. Additionally, the PSS-I was found to have greater diagnostic sensitivity when compared to the CAPS. In sum, the PSS-I appears to be a reliable and valid instrument of PTSD with good diagnostic utility. It is easy to administer and yields both symptom severity and diagnostic information. Disadvantages of the PSS-I include relatively limited evidence of discriminant validity and the assessment of symptoms over the past 2 weeks instead of the past month, which is the time frame required to make a PTSD diagnosis.

The PSS-I has been revised for DSM-5, and the PSS-I-5 [49] has demonstrated initial psychometric merit. Foa et al. [53] provided initial evidence for the internal consistency (alpha = 0.89), test-retest reliability (r = 0.87), interrater reliability (kappa = 0.84), and convergent and discriminant validity of the PSS-I-5 with several other measures of PTSD and related constructs. Although similar to the original PSS-I in structure and format, one notable change is the assessment of symptoms over the past month instead of the past 2 weeks.

Structured Clinical Interview for DSM-IV: PTSD Module

The Structured Clinical Interview for DSM-IV (SCID; [46]) is a comprehensive interview assessing all major psychiatric disorders, including PTSD. The PTSD module of the SCID (SCID-PTSD) may be administered as part of the full interview or independently as a stand-alone measure. In the SCID-PTSD, interviewers ask a trauma exposure screening question followed by 17 questions assessing the 17 PTSD symptom criteria. The interview may be discontinued at the point at which symptom criteria are not met. Each symptom is rated on a three-point scale (1 = absent, 2 = subthreshold, and 3 = threshold, with an additional rating of ? = inadequate information), and a PTSD diagnosis is obtained by counting symptoms rated as present and applying the DSM-IV diagnostic rule. The SCID-PTSD does not yield a PTSD symptom severity score.

The SCID-PTSD historically has been regarded as the gold standard PTSD assessment instrument against which many other measures are compared. In the National Vietnam Veterans Readjustment Study (NVVRS), the SCID-PTSD demonstrated high interrater reliability with coefficients of 0.94 and 0.87 for lifetime and current diagnoses, respectively [80]. It also was found to have strong convergent validity with the Mississippi Scale (kappa = 0.53) and the PK scale of the MMPI (kappa = 0.48) and adequate to excellent sensitivity and specificity (0.81 and 0.89, respectively) when compared against a composite PTSD diagnosis [81]. More recently, the strong reliability of the SCID-PTSD has been replicated by Zanarini and Frankenburg [130] and Lobbestael et al. [83]. In addition to the psychometric evidence for the 17 symptom items, the trauma exposure screening question has also demonstrated good sensitivity and specificity [43]. The SCID was recently revised for DSM-5 (SCID-5, [47]) but information regarding the psychometric properties of the SCID-5 PTSD module is not yet available.

Composite International Diagnostic Interview: PTSD Module

The Composite International Diagnostic Interview (CIDI; [128]) is another comprehensive interview assessing most major psychiatric disorders. The CIDI was intended for use in large epidemiological studies and is based on the Diagnostic Interview Schedule (DIS; [103]). It expands on the DIS, which assesses DSM diagnostic criteria, by also assessing diagnostic criteria of the International Classification of Diseases (ICD), to allow for cross-national comparative studies. A revised and expanded version of the CIDI was introduced by the World Health Organization in 1998, which included a greatly expanded PTSD module that could be administered in conjunction with or independent of the full interview. The PTSD module (CIDI-PTSD) includes a comprehensive assessment of lifetime trauma exposure, 17 items assessing PTSD symptoms, and 2 items assessing trauma-related guilt. The CIDI-PTSD also includes items assessing clinical distress and functional impairment. Each item is rated using a yes/no format. The latest version of the CIDI (CIDI 3.0; [73]) is similar in format and content to its earlier version and is available in more than 30 languages.

Numerous studies have examined the psychometric properties of the various versions of the CIDI (for reviews, see [4, 76, 124]), but fewer studies have examined the psychometric properties of the CIDI-PTSD. In an examination of initial version of the CIDI-PTSD across five sites, Peters et al. [101] found the CIDI-PTSD to demonstrate good internal consistency, with an alpha of 0.76 and 0.86 for the ICD 10 and DSM-III-R diagnostic criteria, respectively. In the same study, the CIDI-PTSD exhibited poor to good concurrent validity with a clinician diagnosis, with kappa of 0.26 and 0.66 for DSM-III-R and ICD 10 diagnoses, respectively. Using the latest version of the CIDI (Version 3.0), Haro et al. [62] found adequate agreement between the CIDI-PTSD and SCID-PTSD (kappa = 0.49 for lifetime prevalence). Similarly, Kimerling et al. [75] found adequate agreement between the CIDI-PTSD and CAPS (kappa = 0.56 for lifetime prevalence). In sum, the CIDI-PTSD appears to demonstrate adequate reliability and concurrent validity. Its structured design is suitable for its intended use in large epidemiological studies, but the yes/no format and lack of symptom severity rating make it less useful in a clinical setting.

Structured Interview for PTSD

The Structured Interview for PTSD (SIP; [37]) is a 19-item structured interview with 17 items corresponding to the 17 PTSD symptom criteria and 2 items assessing trauma-related guilt. The interview was originally introduced as the SI-PTSD [35], but was renamed the SIP at the time of its revision from assessing DSM-III to DSM-IV PTSD criteria. Interviewers ask a series of initial prompts and follow-up questions for each criterion and then rate severity on a five-point scale (0–4). Rating scale anchors are supplemented with descriptors to help clarify the meaning of each rating and reflect a combination of frequency, severity, and functional impairment. The SIP yields current and lifetime symptom severity and diagnostic data. Total symptom severity score is obtained by summing ratings for all 19 items; an alternative symptom severity score corresponding to DSM-IV criteria also may be calculated by excluding the two guilt items. A PTSD diagnosis is obtained by counting the symptoms rated as two or greater as present and applying the DSM-IV diagnostic rule.

SIP scores have demonstrated strong psychometric properties. The original version of the interview has shown high internal consistency (alpha = 0.94), good test-retest (0.71) and interrater (0.97–0.99) reliability, and high diagnostic agreement with the SCID-PTSD (kappa = 0.79) [35]. Similarly, the revised SIP has shown high internal consistency (alpha = 0.80), test-retest reliability (0.89), and interrater reliability (0.90) [37]). In sum, the SIP appears to demonstrate strong psychometric properties. It has the advantage of offering symptom severity and diagnostic information, as well as information about guilt. The major disadvantage of the SIP is the relatively limited number of studies examining its psychometric properties.

Self-Report Measures

DSM Correspondent

PTSD Checklist

The PTSD Checklist (PCL; [114]) is a 17-item DSM-correspondent self-report measure of PTSD. Developed in 1990 at the National Center for PTSD, the PCL was originally based on DSM-III-R criteria, was revised in 1994 for DSM-IV, and recently was revised again for DSM-5. PCL items consist of short phrases reflecting DSM symptom criteria. Respondents are instructed to indicate how much they were bothered by each symptom in the past month, using a five-point (1 = not at all to 5 = extremely) rating scale. There are three versions of the PCL (military, civilian, and specific), which differ only in how the stressful event is labeled in the first eight items, i.e., the items that specifically mention an index event. The military version (PCL-M) refers to “a stressful military experience,” the civilian version (PCL-C) refers to “a stressful experience from the past,” and the specific version (PCL-S) refers to “the stressful experience,” which respondents are instructed to identify before completing the symptom items. The PCL may be used as a continuous measure of PTSD symptom severity for symptom clusters or for the entire PTSD syndrome by summing scores over items within a given cluster or by summing all 17 items. The PCL may also be used to derive a dichotomous PTSD diagnosis by considering each item rated as “2 = moderately” or higher as a symptom endorsed, then following the DSM-IV diagnostic rule.

The PCL is one of the most widely used self-report PTSD measures. It has been thoroughly investigated in a wide range of trauma populations and has excellent psychometric properties [122]. The PCL has been used for screening (e.g., [5]), measuring changes in symptom severity in treatment studies (e.g., [54]), estimating PTSD prevalence (e.g., [65]), and predicting PTSD diagnostic status based on a structured interview (e.g., [14]). The PCL has been the basis for much of the extensive confirmatory factory analytic literature that has identified the symptom structure of PTSD [41] and led to the separation of avoidance and numbing into distinct clusters in DSM-5.

The PCL was recently revised for DSM-5. Notable changes include (a) an increase from 17 to 20 items, with creation of new items and revision of existing items to achieve correspondence with DSM-5 criteria for PTSD, and (b) a change in the rating scale from 1–5 to 0–4. In addition, instead of military, civilian, and specific versions as for the PCL, the PCL-5, like the specific version of the PCL, requires that an index event be identified before responding to symptom items. There are three versions of the PCL-5, one with a brief Criterion A section that helps respondents identify an index event, one with the extended version of the LEC-5, and one without a Criterion A section, for use when an index event has been identified by some other method. Initial studies examining the psychometric properties of the PCL-5 have provided strong evidence for its internal consistency, test-retest reliability, and convergent and discriminant validity [16, 19, 129].

Posttraumatic Stress Diagnostic Scale

The Posttraumatic Stress Diagnostic Scale (PDS; [48]) is the revised version of the Modified Posttraumatic Stress Scale – Self-Report Version (MPSS – SR; [45]), which is a slightly revised version of the original Posttraumatic Stress Scale – Self-Report Version (PSS – SR; [51]). Modifications across the different versions include slight rewording of items, inclusion of frequency and severity ratings, and change in time frame assessed. The most recently modified PDS is a 49-item self-report instrument assessing all six DSM-IV PTSD criteria with 21 items assessing exposure to a traumatic event (Criterion A), 17 items assessing PTSD symptoms (Criterion B–D), 2 items assessing duration (Criterion E), and 9 items assessing functional impairment (Criterion F). Symptoms are assessed over the past month and rated on a four-point scale (0 = not at all or only one time, 1 = once a week or less/once in a while, 2 = two or four times a week/half the time, 3 = five or more times a week/almost always). The PDS yields a continuous symptom severity score and a dichotomous diagnostic score, with items rated as 1 or greater counted as symptoms endorsed.

The PDS has been demonstrated to have strong psychometric properties in several studies. Foa et al. [52] found the PDS to have high internal consistency (alpha = 0.92), good test-retest reliability (0.92), and good diagnostic utility when compared with the SCID-PTSD (sensitivity = 0.89, specificity = 0.75, kappa = 0.65). In the same study, the PDS demonstrated strong convergent validity with another PTSD measure but poor discriminant validity with a depression measure. The reliability, convergent and discriminant validity, and diagnostic utility of PDS scores have more recently been extended to a wide variety of trauma populations [1, 6, 61]. Taken together, the PDS appears to be a well-validated self-report instrument assessing all DSM PTSD criteria.

The PDS was recently revised for DSM-5, with the resulting PDS-5 including 17 items assessing trauma exposure, 20 items assessing PTSD symptoms, 2 items assessing distress and impairment, and 2 items assessing symptom onset and duration. Symptoms are assessed over the past month and rated on a slightly modified four-point scale (0 = not at all, 1 = once a week or less/once in a while, 2 = two or three times a week/somewhat, 3 = four or five or more times a week/very much, and 4 = six or more times a week/severe). An initial study of the PDS-5 provided evidence for internal consistency (alpha = 0.95), test-retest reliability (r = 0.90), and convergent and discriminant validity [53].

Davidson Trauma Scale

The Davidson Trauma Scale (DTS; [33]) is a self-report measure with 17 items corresponding to the 17 PTSD symptoms. Symptoms are assessed over the past week and are rated on separate scales for frequency (0 = not at all, 1 = once only, 2 = two to three times, 3 = four to six times, 4 = every day) and severity (0 = not all distressing, 1 = minimally distressing, 2 = moderately distressing, 3 = markedly distressing, 4 = extremely distressing). The DTS was designed to yield a symptom severity score, but its diagnostic utility also has been examined in several studies.

DTS scores have demonstrated high internal consistency (alpha >0.90 for frequency, severity, and total scores), good test-retest reliability (0.86), and moderate convergent validity with other PTSD measures (0.64–0.78) [36]. The reliability, internal consistency, and convergent and discriminant validity of the DTS have been replicated in several studies (e.g., [1, 91]). Although no scoring rules exist for converting frequency and severity items into symptom counts, several DTS total score cutoffs have been suggested and investigated with regard to diagnostic utility. Cutoff scores of 40 and 32 have indicated high sensitivity and specificity in two separate studies [36, 91]; however, Adkins et al. [1] found the diagnostic utility of the DTS using a cutoff score of 43 to be significantly lower than two other self-report PTSD measures. Thus, the DTS has demonstrated stronger psychometric properties as a continuous symptom severity measure than as a dichotomous diagnostic tool.

Detailed Assessment of Posttraumatic Stress

The Detailed Assessment of Posttraumatic Stress (DAPS; [23]) is a comprehensive 104-item self-report instrument assessing DSM-IV PTSD diagnostic criteria and other trauma-related phenomena. It includes two validity scales assessing positive and negative response bias; four trauma specification scales assessing trauma exposure, onset, peritraumatic distress, and peritraumatic dissociation; four posttraumatic stress scales assessing PTSD symptoms and impairment; and three associated features scales assessing trauma-specific dissociation, substance abuse, and suicidality. PTSD symptoms are assessed for the past month and rated on a five-point Likert scale (1 = never, 2 = less than once a week, 3 = about once a week, 4 = two or three times a week, 5 = four or more times a week). Raw scale scores are converted to T-scores based on a normative sample of trauma survivors, with T>65 indicating a clinically significant elevation. The DAPS yields symptom severity and diagnostic information. Decision rules for making a probable PTSD diagnosis are included in the DAPS professional manual.

The DAPS has strong psychometric properties. Briere [23] found all of the clinical scales to have relatively high internal consistency with alphas ranging from 0.67 to 0.98 with a mean of 0.88. The PTSD symptom scales were strongly correlated with other PTSD scales including the CAPS, PCL , Civilian Mississippi Scale, and Impact of Event Scale (rs = 0.68–0.89) and less strongly correlated with less closely related constructs including measures of depression (0.61–0.78), somatization (0.32–0.47), antisocial personality features (0.23–0.27), and mania (−0.01–0.10). Additionally, the PTSD symptom scales demonstrated strong diagnostic utility when compared with the CAPS (sensitivity = 0.88, specificity = 0.86, kappa = 0.73). Advantages of the DAPS include comprehensive coverage of both core and associated features of PTSD, validity scales, and standardized norms. Disadvantages include its length and the limited number of studies investigating its psychometric properties.

Non-DSM Correspondent

Impact of Event Scale and Impact of Event Scale-Revised

The Impact of Event Scale (IES; [67]) is one of the first self-report measures of posttraumatic responses. It contains 15 items and is based on Horowitz’s [66] conceptualization of reactions to extreme stressors and covers two primary symptom domains, intrusion and avoidance. The scale was revised in 1997 with seven additional items: six items assessing hyperarousal and one item assessing dissociative flashbacks (IES – R; [120]). Symptoms are assessed over the past week and rated on a five-point Likert scale for severity (0 = not at all, 1 = a little bit, 2 = moderately, 3 = quite a bit, 4 = extremely). The IES – R was designed as a continuous measure of symptom severity and does not yield diagnostic information [119].

The original IES has demonstrated adequate reliability and internal consistency [67, 109]; however, its convergent and discriminant validity have been questioned. In a review of 23 studies using the IES, Sundin and Horowitz [109] reported wide variability in the convergent validity between the intrusion and avoidance scales and other measures of PTSD (0.49–0.79 for intrusion, 0.29–0.80 for avoidance). A similar pattern of psychometric characteristics has been found for the IES – R, with evidence supporting its reliability and internal consistency [1, 9, 120], but questioning its convergent validity (e.g., [9]). Additionally, the IES – R hyperarousal items have demonstrated lower internal consistency and reliability than the intrusion and avoidance items [7, 9]. In reference to the convergent validity of the IES – R, Beck et al. [9] noted that the seemingly low convergent validity of the IES – R with other measures of PTSD may not necessarily reflect poorly on its psychometric properties, but rather reflect differences in content coverage.

Unlike many other measures of PTSD, the IES – R was not designed to correspond directly to the DSM PTSD criteria and does not directly assess all 17 PTSD symptom criteria (e.g., sense of foreshortened future, diminished interest). The relatively limited coverage of posttraumatic stress responses provided by IES – R items is its main disadvantage. Advantages include its popularity in clinical research and translation into a number of different languages.

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