Reliability and validity of the PDS and PSS-I among participants with PTSD and alcohol dependence

Journal of Anxiety Disorders 26 (2012) 617–623

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Journal of Anxiety Disorders

Reliability and validity of the PDS and PSS-I among participants with PTSD and alcohol dependence Mark B. Powers a,∗ , Seth J. Gillihan b , David Rosenfield a , Alissa B. Jerud c , Edna B. Foa b a b c

Southern Methodist University, United States University of Pennsylvania, United States University of Washington, United States

a r t i c l e

i n f o

Article history: Received 12 August 2011 Received in revised form 26 January 2012 Accepted 13 February 2012 Keywords: PTSD PDS PSSI Alcohol dependence Prolonged exposure therapy

a b s t r a c t The prevalence of alcohol use disorder (e.g., alcohol dependence; AD) among individuals with posttraumatic stress disorder (PTSD) is quite high, with estimates of 52% for men and 30% for women (Kessler, Sonnega, Bromet, Hughes, & Nelson, 1995). There are several interviews and self-report measures of PTSD with good published psychometric properties, and they are routinely used with comorbid AD and PTSD. However, none of these instruments was validated with this population. The current study fills this gap by examining the psychometric properties of the PTSD Symptom Scale-Interview (PSS-I) and the self-report PTSD Diagnostic Scale (PDS) in individuals diagnosed with current PTSD and AD. Both scales comprised of 17 items provide diagnostic and symptom severity information according to DSM-IV-TR criteria. Participants were 167 individuals who were diagnosed with AD and chronic PTSD and were enrolled in a randomized controlled treatment study. Results revealed excellent internal consistency of both the PSS-I and the PDS, good test–retest reliability over a 1-month period, and good convergent validity with the SCID. The specificity of the PSS-I diagnosis of PTSD was better than the PDS diagnosis, the latter exhibiting a greater percentage of false positives. In sum, the results showed that the PSS-I and PDS performed well in this population and can be used with confidence to assess PTSD diagnosis and symptom severity. © 2012 Elsevier Ltd. All rights reserved.

Posttraumatic stress disorder (PTSD) is a common psychiatric disorder, with lifetime risk of approximately 8.7% in the general population (Kessler et al., 2005). Individuals with PTSD are at substantially increased risk for alcohol abuse and alcohol dependence (AD); the risk for men with PTSD is double that of men without PTSD, while women with PTSD are 2.5 times as likely to have alcohol abuse or dependence (Kessler et al., 1995). Indeed, alcohol abuse and dependence are the most common substance use disorders among individuals with PTSD (Kessler et al., 1995). Importantly, comorbid AD–PTSD is not only common but also is associated with a more complex clinical presentation and poorer treatment outcome than either AD or PTSD alone (Ouimette, Ahrens, Moos, & Finney, 1997). For example, compared to patients with AD alone, PTSD–AD patients have more severe addictions, comply less with treatment, and are quicker to relapse (Brady, Back, & Coffey, 2004; Brown, Stout, & Mueller, 1996). Similarly, in comparison to individuals with PTSD alone, AD–PTSD patients tend to have greater PTSD symptom severity as well as a wider range of PTSD symptoms (Ouimette, Wolfe, & Chrestman, 1996). Finally, comorbid AD–PTSD

∗ Corresponding author. E-mail address: [email protected] (M.B. Powers). 0887-6185/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.janxdis.2012.02.013

is associated with more interpersonal and social support problems compared to PTSD or SUDs alone (Drapkin et al., 2011; Najavits et al., 1998). The frequent co-occurrence of AD and PTSD and the clinical implications of such comorbidity have spurred a great deal of research aimed at improving current protocols for treating comorbid AD–PTSD. Although limited in number, treatments that address both AD and PTSD have been promising, yielding better treatment outcomes than programs that provide only AD treatment (Back, Brady, Sonne, & Verduin, 2006). These findings suggest that the detection of both disorders in AD–PTSD patients is crucial to maximizing treatment results. To treat comorbid PTSD in an AD population one must first detect it. Indeed, Ouimette, Moos, and Brown (2003) suggest that clinicians routinely screen for trauma and PTSD among SUD patients. In addition, it is crucial that treatment trials use outcome measures that have been rigorously tested and found to be psychometrically sound with the target population. One concern is that the psychometric data reported for measures designed to assess PTSD symptoms have been collected in studies where participants with substance use disorders were largely excluded. Thus, the previously reported strong psychometric properties may not generalize to this/comorbid PTSD–AD population.

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It is often assumed that once an instrument has demonstrated adequate psychometric properties, these findings will generalize to all future applications (Henson, 2001; Vacha-Haase, Kogan, & Thompson, 2000). However, Thompson (1994) and Wilkinson and the American Psychological Association’s Task Force on Statistical Inference (1999) and the special section of Educational and Psychological Measurement (April 2000) state that the psychometrics observed in one population cannot be assumed to generalize to new populations. They highlight that it is inaccurate to describe the psychometrics of “the test”, but rather, the psychometrics of the scores with a given population. Thus, psychometrics obtained with a PTSD only sample may not generalize to individuals with both AD and PTSD. There are several reasons to believe such a generalization may be hazardous. For example, habitual heavy drinking significantly alters the symptom profile of PTSD due to the depressant effects of ethanol on the central nervous system. In addition, alcoholism contributes to the reduced hippocampal volume in PTSD, which in turn, is associated with poor cognitive/intellectual functioning that may impact psychometric properties of PTSD measures (Gurvits et al., 1996,2000; Hedges & Woon, 2010; McNally & Shin, 1995; Pitman, Orr, Lowenhagen, Macklin, & Altman, 1991; Stein, Koverola, Hanna, Torchia, & McClarty, 1997; Vasterling, Brailey, Constans, & Sutker, 1988). Without assessing the psychometrics of PTSD measures in the context of comorbid alcohol dependence and PTSD, they cannot be assumed to be reliable and valid. Two instruments that are frequently used for assessing the presence and severity of PTSD symptoms are the Posttraumatic Symptom Scale-Interview (PSS-I; Foa, Riggs, Dancu, & Rothbaum, 1993) and the Posttraumatic Diagnostic Scale (PDS; Foa, Cashman, Jaycox, & Perry, 1997). Whereas the PSS-I is a semi-structured interview, the PDS is a self-report measure, and thus the two measures are often used in conjunction in order to obtain the most reliable assessment of posttraumatic symptoms. The PSS-I and the PDS assess both the presence and severity of the 17 PTSD symptoms outlined in the Diagnostic and Statistical Manual of Mental Disorders (4th ed., text revision; American Psychiatric Association, 2000). Reliability and validity of the PSS-I and the PDS have been evaluated in several populations (without comorbid alcohol dependence) including female sexual assault survivors (PSS-I; Foa et al., 1993), men and women who have experienced a wide range of traumatic events (PSS-I; Foa & Tolin, 2000), and men and women who have experienced a high-magnitude stressor (PDS; Foa et al., 1997). For example, in a sample of 118 recent rape and nonsexual assault victims, the PSS-I was found to have strong internal consistency (Cronbach’s alpha = .85) and 1-month test–retest reliability (r = .80); the PDS had similarly strong psychometric properties with Cronbach’s alpha = .91 and 1-month test–retest reliability of r = .74 (Foa et al., 1993). Similarly, in a sample of 64 individuals with a wide range of traumatic events the internal consistency of the PSS-I was high (Cronbach’s alpha = .86) and the agreement between interviewers and raters of the videotaped interviews was very high (r = .93). Foa et al. (1997) found a Cronbach’s alpha of .92 and 2–3-week test–retest reliability of r = .83 for the PDS among a large sample (n = 248) of mixed trauma survivors (Foa et al., 1997). While the PSS-I and the PDS have been found to be reliable and valid tools for assessing PTSD, the psychometric properties of these two measures have yet to be tested in a sample of patients with comorbid AD and PTSD. The purpose of the present study, therefore, was to replicate and extend the previous findings related to the PSS-I and the PDS by evaluating the psychometric properties of both measures within a sample of comorbid AD and PTSD patients. To this end, we administered both instruments along with the Structured Clinical Interview for DSM-IV (SCID; First, Spitzer, & Gibbon, 1994) which assessed the presence of a criterion A event (i.e., the individual witnessed, experienced, or was confronted with a traumatic event that evoked intense fear, helplessness or horror)

as well as for criterion E-defined duration (i.e., whether the individual’s PTSD symptoms had been present for at least one month prior to assessment). 1. Method 1.1. Participants Participants in the current study were 167 individuals (58 females) who were diagnosed with AD and chronic PTSD and were enrolled in a treatment study (Foa & Williams, 2010). Participants met DSM-IV-TR (APA, 2000) criteria for AD and PTSD following a variety of traumas. All participants were 18–65 years old (mean = 42.6, SD = 9.8) and reported heavy alcohol drinking in the past 30 days, defined as 12 or more drinks (0.6 oz of ethanol) per week. The average length of time elapsed between participants’ index trauma and the initial assessment was 11.5 years (M = 11.58, SD = 13.02). Most participants were African-American (n = 107, 64.1%) or White (n = 50, 29.9%) with highest education level primarily including some college (n = 59, 35.3%), high school graduation (n = 61, 36.5%), or some high school (n = 20, 12.0%). Further participant information is presented elsewhere (Foa & Williams, 2010). 1.2. Measures 1.2.1. PTSD Symptoms Scale-Interview (PSS-I) The PSS-I (Foa et al., 1993) is a 17-item semi-structured interview that assesses for three clusters of PTSD symptoms: reexperiencing (five items), avoidance (seven items), and arousal (five items). Each item corresponds to one of the 17 DSM-IV-TR (APA, 2000) diagnostic criteria for PTSD. For each item on the PSS-I, the interviewer rates severity within the past 2 weeks using a 4-point scale: 0 = not at all/0 times per week, 1 = a little bit/once per week, 2 = somewhat/2-4 times per week, and 3 = very much/5 or more times per week. A score of one or greater was required in order for the symptom to be considered present. Overall severity was calculated using the sum of the severity ratings for each of the 17 items. Individuals who endorsed at least 1 reexperiencing, 3 avoidance and 2 arousal symptoms were diagnosed with PTSD (American Psychiatric Association, 2000). In our prior study (Foa et al., 1993), Cronbach’s alpha for the full scale was .85. For the symptom cluster subscales, alpha coefficients were as follows: reexperiencing .69, avoidance .65, and arousal .71. Test–retest reliability of the overall severity score was .80. 1.2.2. Posttraumatic Diagnostic Scale (PDS) The PDS (Foa et al., 1997) is a 17-item self-report measure that is based on the PSS-I (Foa et al., 1993), and that inquires about trauma exposure and functioning. In the present study, PTSD symptom severity was scored using the same procedures as those used for scoring the PSS-I. In our prior study (Foa et al., 1993), Cronbach’s alpha was .91 for total symptom severity. For the symptom cluster subscales, alpha coefficients were as follows: reexperiencing .78, avoidance .80, and arousal .81. Test–retest reliability of the overall severity score was .74. 1.2.3. Structured Clinical Interview for DSM-IV (SCID) The SCID (First et al., 1994) is a standardized diagnostic interview that is widely used to assess psychiatric disorders. 1.2.4. State–Trait Anxiety Inventory (STAI) The STAI (Spielberger, Gorsuch, Lushene, Vagg, & Jacobs, 1983) contains 40 items, 20 for state anxiety and 20 for trait anxiety. Spielberger et al. reported that test–retest reliability for trait anxiety was

M.B. Powers et al. / Journal of Anxiety Disorders 26 (2012) 617–623

.81; as expected, figures were lower for state anxiety (.40). Internal consistency ranges from .83 to .92. 1.2.5. Beck Depression Inventory (BDI) The BDI (Beck, Ward, Mendelson, Mock, & Erbaugh, 1961) is a 21-item inventory measuring depressed mood and vegetative symptoms of depression. The inventory had a split-half reliability coefficient of .93. Correlations with clinical ratings of depression range from .62 to .66. 1.3. Procedure Participant recruitment was accomplished primarily through public advertising and professional referrals. Prospective participants contacted the intake coordinator, who screened individuals to assess eligibility. Participants that seemed eligible on the basis of the screen were invited to attend an intake session that included medical history, physical examination, an electrocardiogram (ECG), routine laboratory tests, and a psychiatric diagnostic interview (SCID); the SCID was administered by a doctoral-level psychologist. At the pre-treatment assessment, an independent evaluator (IE) who was not involved in the screening or treatment activities administered the PSS-I. Participants were randomly assigned to receive naltrexone or placebo, and randomly assigned to receive Prolonged Exposure (PE) therapy or no PE. Patients in all treatment conditions received 18 30-min visits with the study nurse who dispensed medication, monitored adherence, provided education about alcohol dependence, gave supportive counseling, and provided direct advice concerning drinking. Visits took place weekly during the first 3 months of the trial and bi-weekly during the remaining 3 months. The PE condition consisted of 12 weekly sessions of 1.5–2 h, followed by 6 bi-weekly sessions. Each PE session began with a review of the homework assignment and presentation of the agenda for that session, and ended with assignment of homework (see Foa, Hembree, & Rothbaum, 2007). IEs were blind to treatment conditions. Patients were assessed at pretreatment, posttreatment and every 4 weeks during the follow-up phase. Here, we report the results of assessments at weeks 20 and 24. We chose these two assessment points for the following reasons. First, because of study design, all participants were diagnosed with PTSD at the inception of the study. Thus, we expected a restricted range in PTSD symptoms during the early assessments, which would limit the ability to evaluate the measures’ sensitivity and specificity of diagnoses. Second, we chose not to use later assessment points in order to maximize our sample size, which decreased over time due to attrition. Third, all the measures of interest were administered at these two particular assessment visits. Finally, we expected that the effects of the ongoing treatment would have stabilized by week 20. Thus, week 20 would produce a relatively stable baseline from which to examine test–retest reliability, given that ongoing treatment would not contribute substantial additional variance to later assessments. All results reported were calculated using the PSS-I and PDS scores from the 116 participants who were assessed at week 24 (although, not all participants completed all measures). The test–retest reliability of the PSS-I and PDS was computed using data from weeks 20 and 24. No study-related PTSD treatment was delivered between these time points. 2. Results 2.1. Internal consistency Cronbach’s alpha on the PSS-I scores at week 24 was .90. The average item–total correlation for the 17 items was .57. Item #8, “Are there parts of the trauma you cannot remember?” had an

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item–total correlation of .13; the range of item–total correlations for the remaining 16 items was .47–.74, with an average of .60. Alpha coefficients for the symptom cluster subscales were: reexperiencing .85, avoidance .82, and arousal .74. Cronbach’s alpha for the PDS scores was .95. The average item–total correlation for the PDS was .72, with a range of .47–.85. Interestingly, the lowest item–total correlation, .47, was again found for item #8. The range for the remaining 16 items was .58.85 with a mean of .74. Alpha coefficients for the subscales were: .92, .91, and .88 for reexperiencing, avoidance, and arousal scales, respectively. 2.2. Test–retest reliability Test–retest reliability for the PSS-I over a 1-month period (weeks 20 and 24) was evaluated using Pearson correlations. Data from the 101 participants who were interviewed for the PSS-I at both time points were included in these analyses. The total score of the PSS-I revealed a test–retest correlation of r(101) = .80, p < .001. The test–retest correlations for the three clusters were: reexperiencing r(101) = .55, p < .001; avoidance r(101) = .79, p < .001; and arousal r(101) = .78, p < .001. One-month test–retest reliability of the PDS was calculated using data from 105 participants who completed the PDS at both time points. The test–retest of the overall severity score was r(105) = .85, p < .001. The test–retest reliability for the three clusters were: reexperiencing r(105) = .79, p < .001; avoidance r(105) = .85, p < .001; and arousal r(105) = .75, p < .001. 2.3. Interrater reliability Interrater agreement on the PSS-I was assessed on 21 participants whose audio recorded interviews were selected at random and scored by 3 raters; the interviews were conducted at various assessment points during the study. Agreement was examined for PTSD diagnosis and overall severity. Kappa for the agreement on the PTSD diagnosis was .79, with all raters agreeing on the diagnosis for 18 out of the 21 participants (86%). ICC for the total severity score was .73. 2.4. Concurrent validity The relation among the PSS-I, PDS, STAI, and the BDI were assessed using Pearson correlation coefficients. Data were again collected at week 24. A total of 113 participants completed the PSSI and 116 completed the PDS, but a few of these did not complete the entire STAI or the BDI (see degrees of freedom for each correlation below for the number completing each pair of variables). Correlation coefficients are presented in Table 1. The PSS-I total severity score was significantly correlated with all the other measures of symptoms: PDS total score, r(111) = .78, p < .001; STAI state, r(108) = .63, p < .001; STAI trait, r(106) = .67, p < .001; and BDI, r(112) = .76, p < .001. Each of the three PTSD cluster scores from the PSS-I also was correlated significantly with these same measures: Correlations with the BDI, STAI trait, and STAI state measures ranged from .51 to .71, all ps < .001. Similarly, the cluster scores were also highly related to PDS total score, with rs of .70, .70, and .66, ps < .001, for reexperiencing, avoidance, and arousal, respectively. The PDS total score was significantly correlated with all of the other psychological symptoms: STAI state, r(110) = .66, p < .001; STAI trait, r(108) = .67, p < .001: and BDI, r(115) = .84, p < .001. Cluster scores from the PDS were also significantly related to all of the other self-report measures of symptoms, with correlations ranging from .55 to .83, ps < .001. The correlations between the PDS cluster

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Table 1 Correlation coefficients relating PTSD symptom scale scores to other measures of psychopathology.

1. PSS-I total 2. PSS-I re-experiencing 3. PSS-I avoidance 4. PSS-I hyperarousal 5. PDS total 6. PDS re-experiencing 7. PDS avoidance 8. PDS hyperarousal 9. STAI-state 10. STAI-trait 11. BDI

1

2

3

4

5

6

7

8

– – – – .78 .67 .72 .76 .63 .67 .76

– – – – .70 .73 .61 .62 .51 .51 .58

– – – – .70 .67 .72 .76 .54 .61 .71

– – – – .66 .49 .57 .76 .61 .64 .68

– – .87 .66 .67 .84

– – –

– – – .68 .65 .83

– – –

.56 .59 .71

9

.63 .55 .74

– .91 .71

10

– .75

Note: All correlations are significant at p < .001.

scores and the PSS-I total scores were .67, .72, and .76, ps < .001, for reexperiencing, avoidance, and arousal, respectively. 2.5. Convergent validity 2.5.1. Comparison of PSS-I and PDS to SCID diagnosis PTSD diagnoses based on the PSS-I and PDS were compared to those based on the SCID. There was substantial agreement between the PSS-I and the SCID, as indicated by the kappa coefficient of agreement,  = .75. Of the 88 participants who completed the PSS-I and the SCID, 29 (33%) met diagnostic criteria on the SCID, and 31 (35%) met criteria on the PSS-I (see Table 2). Twenty-five (86%) of the 29 who were diagnosed by the SCID also met criteria on the PSS-I (i.e., sensitivity of the PSS-I = 86%). Similarly, 53 (90%) of the 59 participants who did not meet criteria on the SCID also did not meet criteria on the PSS-I (i.e., specificity of the PSS-I was 90%). There was moderate agreement between the PTSD diagnosis based on the PDS and that based on the SCID. The kappa coefficient of agreement between the two was .44. Of the 90 participants who completed both measures, 31 (34%) met diagnostic criteria on the SCID and 49 (54%) met criteria on the PDS (Table 2). Twentyseven (87%) of the 31 meeting criteria on the SCID also met criteria on the PDS (sensitivity = 87%), while 37 (63%) of those who failed to meet criteria on the SCID also failed to meet criteria on the PDS (specificity = 63%).

subjects did not meet diagnostic criteria based on the PSS-I, while 53 (48%) did not meet criteria on the PDS. Of the 73 who did not meet PTSD criteria on the PSS-I, 51 (70%) also did not meet criteria on the PDS (specificity = 70%). Pearson correlation coefficients between scores on the PSS-I and PDS were calculated for the 111 participants who completed both measures (see Table 1). As reported above, the correlation for the total PTSD severity score on the two scales was r(111) = .78, p < .001. Correlations between the cluster scores of the PSS-I and those of the PDS were as follows: reexperiencing, r(111) = .73, p < .001; avoidance, r(111) = .72, p < .001: and arousal, r(111) = .76, p < .001. Examination of the individual symptoms on the PSS-I and PDS indicated that more symptoms were endorsed via the self-report than via the interview (see Table 4). Participants reported more symptoms on 16 of the 17 symptom questions, with the difference being significant on 6 of those 16. The only symptom with higher scores on the PSS-I than the PDS concerned being overly alert; this difference was significant, t(110) = 1.98, p = .05. Thus, total scores on the PDS (M = 15.4, SD = 13.1) were higher than on the PSS-I (M = 13.1, SD = 11.4), t(110) = 2.94, p < .005; the same pattern emerged for the reexperiencing cluster scores (M = 3.4, SD = 3.6 vs. M = 2.4, SD = 3.2), t(110) = 4.02, p < .001, and on the avoidance cluster scores (M = 6.4, SD = 6.0 vs. M = 5.3, SD = 5.3), t(110) = 2.63, p = .01. No significant differences between the PDS and the PSS-I was found on the arousal cluster scores: (M = 5.5, SD = 4.6 vs. M = 5.3, SD = 4.4), t(110) = 0.70, p = .49.

2.6. Comparison between the PSS-I and the PDS 3. Discussion Agreement of the diagnosis of PTSD based on the PSS-I and the PDS was examined with data from the 111 subjects assessed at week 24 who completed both the PSS-I and the PDS. The kappa coefficient for agreement of PTSD diagnosis was .57. Thirty-eight (34%) of the 111 subjects met diagnostic criteria for PTSD according to the interview (PSS-I), while 58 (52%) met diagnostic criteria on the PDS (see Table 3). Sensitivity analysis indicated that 36 (95%) of the 38 diagnosed with PTSD by the PSS-I were also diagnosed with PTSD on the basis of the PDS (sensitivity = 95%). Seventy-three (66%) of the 111 Table 2 Agreement of PTSD diagnoses on the SCID, PSS-I, and PDS.

The current paper presented results on the psychometric properties of the self-report and interview versions of the PTSD Symptom Scale—instruments that assess PTSD diagnosis and PTSD severity and its component clusters (reexperiencing, avoidance, and arousal)—among a sample of alcohol-dependent individuals who participated in a treatment study. Overall, the results showed the robustness of the PDS and PSS-I across comorbidity in this new population. More specifically, the results of this study confirm earlier reports (Foa et al., 1993; Foa & Tolin, 2000) on the strong psychometric properties of the PDS and PSS-I and their utility for assessing PTSD severity and diagnosis. Importantly, these results demonstrate that the strong psychometric properties of the PDS

SCID PTSD diagnosis

PSS-I diagnosis of PTSD Absent Present PDS diagnosis of PTSD Absent Present

Table 3 Agreement of diagnoses of PTSD on the PSS-I and the PDS.

Absent n (column%)

Present n (column%)

53 (90%) 6 (10%)

4 (14%) 25 (86%)

PDS diagnosis of PTSD

37 (63%) 22 (37%)

4 (13%) 27 (87%)

Absent Present

PSS-I PTSD diagnosis Absent n (column%)

Present n (column%)

51 (70%) 22 (30%)

2 (5%) 36 (95%)

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Table 4 Mean, standard deviation, and % endorsing each item on the PSS-I and PDS. Symptom

PSS-I (interview) % Endorsing

Reexperiencing 1. Intrusive thoughts 2. Nightmares 3. Flashbacks 4. Emotionally upset 5. Physical reactivity Subscale total (SD) Avoidance 6. Trying not to talk 7. Avoid activities 8. Cannot remember 9. Loss of interest 10. Emotional distance 11. Restricted affect 12. Future plans Subscale total (SD) Hyperarousal 13. Trouble sleeping 14. Irritable 15. Concentration 16. Overly careful 17. Jumpy Subscale total (SD) Severity total (SD)

PDS (self-report) Mean (SD)

% Endorsing

Mean (SD)

39.8 25.7 12.5 39.8 37.2 61.1

.68 (.97) .37 (.70) .18 (.55) .65 (.92) .54 (.82) 2.42 (3.16)

53.0 44.3 44.7 55.3 42.6 66.1

.72 (.81) .58 (.76)** .58 (.74)*** .82 (.90)* .70 (.95)* 3.39 (3.63)

37.2 36.3 23.0 34.5 44.2 35.4 34.5 86.7

.88 (1.25) .85 (1.22) .37 (.76) .74 (1.11) .98 (1.20) .68 (1.01) .82 (1.19) 5.32 (5.44)

53.0 47.0 36.5 58.8 60.0 47.8 49.6 74.8

.99 (1.15) .95 (1.18) .63 (.96)** 1.02 (1.03)** 1.14 (1.10) .81 (1.01) .90 (1.06) 6.44 (6.00)

55.8 38.9 49.6 48.7 39.8 80.5 86.7

1.31 (1.30) .86 (1.19) 1.11 (1.25) 1.22 (1.38) .83 (1.13) 5.33 (4.40) 13.10 (11.41)

69.0 58.6 60.3 54.3 53.4 82.8 88.7

1.43 (1.18) .96 (1.02) 1.13 (1.10) 1.02 (1.15)* .99 (1.14) 5.54 (4.61) 15.41 (13.10)

Note: Means with asterisks are significantly different from the comparable mean for PSS-I. * p ≤ .05. ** p ≤ .005. *** p ≤ .001.

and PSS-I found in earlier reports hold up in a sample of individuals with comorbid alcohol dependence; thus the PDS and PSS-I are valid and reliable instruments for assessing PTSD in this population, both as PTSD screening (particularly the self-report PDS) and as a measure of PTSD severity. The total symptom severity and subscale scores demonstrated good to excellent internal consistency, with total symptom severity coefficients alpha of .90 for the PSS-I and .95 for the PDS. These results are very similar to those obtained by Foa et al. (1993), who also found a marginally higher alpha value for the self-report measure (PS-SR, the precursor of the PTSD; .91) versus the PSS-I (.85). Average item–total correlations for the scales also were similar to those found by Foa et al., with correlations of .57 (PSS-I) and .72 (PDS) in the current sample versus their average correlations of .45 and .60 in the previous study, respectively. As with the earlier paper, the item about psychogenic or dissociative amnesia (Item 8, “Are there parts of the trauma you cannot remember?”) demonstrated the lowest correlation with the full-scale score (.11 for the PSS-I and .47 for the PDS). Interestingly, this finding is consistent with previous psychometric evaluations of the PDS, PSS-I, and the PTSD Checklist (PCL; Blanchard, Jones-Alexander, Buckley, & Forneris, 1996; Foa et al., 1997, 1993). This repeated finding has received little attention in the literature and we can only speculate on potential explanations. First, it may be difficult for patients or evaluators to determine that “important” gaps exist in the trauma memory or to report the absence of something that they cannot remember. Second, it is possible that for some patients the memory gap would be distressing whereas for others, being able to remember everything about the trauma may add to their distress and PTSD symptoms. Thus these opposing effects of psychogenic amnesia on PTSD symptoms could attenuate the correlation of this item with the scale total. Future research may help determine why the presence of psychogenic amnesia is not strongly associated with severity of PTSD symptoms. The test–retest reliability of the measures (total and subscales) over a 1-month span also ranged from good to excellent, with

correlations of .80 and .85 for total symptom severity on the PSSI and PDS, respectively. Interrater agreement was strong, with a kappa for PTSD diagnosis on the PSS-I of .79 (interrater agreement is not calculated for self-report measures like the PDS). These results demonstrate that scores on the PDS and PSS-I are stable over time and across raters (for the PSS-I) among this comorbid sample. The high correlations between both instruments and other measures of psychological distress (STAI and BDI) demonstrate the concurrent validity of the PDS and the PSS-I; thus a greater magnitude of PTSD symptoms tends to go hand in hand with greater general anxiety as well as more depressive symptoms. The correlations obtained in the current study were of similar magnitude as those reported by Foa et al. (1993); for example, Foa et al. found a correlation between the PSS-I and the BDI of r = .72 while the current study found a correlation of r = .76. Similarly, Foa et al. reported a PDS–BDI correlation of r = .80 compared to the current study’s correlation of r = .84. It should be noted that the correlation between the PDS and PSS-I was of similar magnitude to the correlations between these measures and the measures of general anxiety (STAI) and depression (BDI). However, this finding is expected given previous research and the strong symptom overlap among PTSD, depression, and anxiety. For example, the Clinician-Administered PTSD Scale (CAPS) is correlated .61–.75 with measures of depression and .66–.76 with measures of anxiety (Weathers, Keane, & Davidson, 2001). The PSS-I demonstrated excellent convergent validity with the PTSD module of the SCID, with a kappa coefficient of .75; sensitivity (.86) and specificity (.90) were excellent. Foa et al. (1993) did not report kappa coefficients, thus precluding a comparison of the current findings with those of this earlier study. However, this result is in line with the upper range of kappa coefficients reported by Foa and Tolin (2000) between the PSS-I and the Clinician-Administered PTSD Scale (CAPS) (Blake et al., 1990), another commonly used valid and reliable measure of PTSD severity. This value is also higher than the kappa coefficient of .49 reported by Haro et al. (2006) for PTSD diagnosis based on the SCID and the Composite International

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Diagnostic Interview (CIDI) used in the National Comorbidity Survey (Haro et al., 2006; WHO, 1997). Convergent validity for the PDS was lower than for the PSS-I, with kappa = .44. This number is comparable to the kappa coefficient reported by Haro et al. for SCIDCIDI agreement, but somewhat lower than the SCID-PDS agreement (kappa = .65) reported by Foa et al. (1997). Sensitivity for the PSD in the current study was similar to that obtained for the PSS-I (.87 for PDS, .86 for PSS-I), whereas specificity was lower (.63 for PDS, .90 for PSS-I). This greater sensitivity versus specificity supports the use of the PDS as a screening tool for PTSD where “misses” may be more problematic than “false alarms.” Symptom-based diagnostic agreement between the PSS-I and the PDS was acceptable, with a kappa of .57. The PSS-I had a lower rate of PTSD diagnoses versus the PDS, with 34% diagnosed with PTSD based on the PSS-I and 52% based on the PDS. These results are consistent with the lower specificity reported above for the PDS, and were driven by the higher scores on the PDS versus the PSS-I on 16 of the 17 symptoms, leading to higher scores on the PDS for the reexperiencing and avoidance clusters as well as for total symptom severity. These results stand in contrast to the findings of Foa et al. (1993) who reported consistently greater percent endorsement and mean ratings associated with the PSS-I versus the PDS. It is possible that differences in the samples account for this discrepancy; Foa et al. examined a sample of female survivors of rape and nonsexual assault, whereas the current sample comprised both males and females with a broad range of Criterion A events. It could be that women (making up a larger proportion of the sample in previous studies) are more willing than men to disclose their symptoms to the interviewers. However, post hoc analyses of the data from the current study suggested this was not the case. Men and women both endorsed fewer symptoms on the interview version (PSS-I) with no gender by version interaction [F (1, 109) = 0.002, p = .97]. Further research is needed to understand why PDS scores were higher than PSS-I scores in the current study. Additionally all participants in the current sample were alcohol dependent at the time of entry into the treatment study. Whatever the cause of the relatively higher mean scores on the PDS, it is important to consider the possibility that PDS scores may be somewhat higher than scores based on the PSS-I. Although the overall scores were significantly different, the correlation between total PTSD severity scores as measured by the PDS and PSS-I was high (r = .78), indicating that while the absolute scores may have been somewhat higher on the PDS, the relative ranking of individuals’ PTSD severity scores were very similar across the two measures. Finally, we also compared the variability (standard deviation) of the PDS total score in this sample to that found in previous research. We were able to find only one other investigation that reported the standard deviation of the PDS in their sample (Foa et al., 1997). That study reported standard deviations for a sample of individuals who had experienced a “wide variety of traumas” (e.g., combat, assault, fire, abuse, etc.). The variability of PDS scores in the Foa et al. (1997) sample was similar, but slightly higher, than in the present study (SD = 14.7 vs. 13.1, respectively, for total severity; SD = 4.4 vs. 3.6 for the re-experiencing subscale; SD = 6.6 vs. 6.0 for the avoidance subscale; and SD = 5.0 vs. 4.6 for the arousal subscale). Thus, the PDS seems to again perform similarly on this sample of alcoholdependent patients as it did in the initial studies validating the scale. Strengths of the current study include the use of both the selfreport and interview versions of the PSS-I, the use of a validated structured interview (SCID) for comparative diagnostic information, and the demographically diverse sample. The examination of a treatment-seeking sample of individuals with a history of comorbid PTSD and alcohol dependence represents both a strength and a limitation; on one hand, it extends the utility of the PDS and PSS-I to this population while on the other hand it cannot

be known with certainty the extent to which the results reported here apply to other populations. However, the generally close correspondence between the current results and those reported by Foa et al. (1993) suggests that the present findings are broadly applicable across a wide range of populations. Future studies may assess the psychometric properties of these measures with other comorbid populations. 4. Conclusion In sum, the present study showed that the PDS and PSS-I accurately assess PTSD symptoms in populations with comorbid PTSD and alcohol dependence. These data extend our knowledge about the psychometric properties of the PSS-I and PDS, demonstrating that these instruments are valid and reliable measures of PTSD diagnosis and severity among individuals with comorbid PTSD and AD. The PSS-I requires on average approximately one-third less time to administer than does the CAPS (22 min vs. 33 min; Foa & Tolin, 2000), suggesting that considerable savings in time may be associated with the use of this measure compared to other available measures with similar psychometric properties. Thus the PSS-I and PDS may be good choices for use in a wide range of populations both in research settings when rigorous measures of PTSD diagnosis and symptom severity are required as well as in screening settings—for example, following a large-scale natural disaster—when persons who may have PTSD need to be identified accurately and efficiently. Acknowledgments This study was supported by National Institute on Alcohol Abuse and Alcoholism, Grant 5R01 AA012428. ClinicalTrials.gov identifier: NCT00006489. References American Psychiatric Association. (2000). Diagnostic and statistical manual for mental disorders (4th ed. text revision (DSM-IV-TR)). Washington, DC: American Psychiatric Press. Back, S. E., Brady, K. T., Sonne, S. C., & Verduin, M. L. (2006). Symptom improvement in co-occurring PTSD and alcohol dependence. Journal of Nervous and Mental Disease, 194(9), 690–696. Beck, A. T., Ward, C. H., Mendelson, M., Mock, J., & Erbaugh, J. (1961). An inventory for measuring depression. Archives of General Psychiatry, 4, 561–571. Blake, D. D., Weathers, F. W., Nagy, L. M., Kaloupek, D. G., Klauminzer, G., Charney, D., et al. (1990). A clinician rating scale for assessing current and lifetiime PTSD: the CAPS-1. The Behavior Therapist, 13, 187–188. Blanchard, E., Jones-Alexander, J., Buckley, T., & Forneris, C. (1996). Psychometric properties of the PTSD Checklist (PCL). Behaviour Research and Therapy, 34, 669–673. Brady, K. T., Back, S., & Coffey, S. F. (2004). Substance abuse and posttraumatic stress disorder. Current Directions in Psychological Science, 13, 206–209. Brown, P. J., Stout, R. L., & Mueller, T. (1996). Posttraumatic stress disorder and substance abuse relapse among women: a pilot study. Psychology of Addictive Behaviors, 10(2), 124–128. Drapkin, M., Yusko, D., Yasinski, C., Oslin, D., Hembree, E., & Foa, E. (2011). Baseline functioning among individuals with posttraumatic stress disorder and alcohol dependence. Journal of Substance Abuse Treatment, 41, 186–192. First, M. B., Spitzer, R. L., & Gibbon, M. (1994). Structured clinical interview for DSM-IV disorders, SCID-I. New York: Biometrics Research. Foa, E. B., Cashman, L., Jaycox, L., & Perry, K. (1997). The validation of a self-report measure of posttraumatic stress disorder: the posttraumatic diagnostic scale. Psychological Assessment, 9(4), 445–451. Foa, E. B., Hembree, E. A., & Rothbaum, B. O. (2007). Prolonged exposure therapy for PTSD: emotional processing of traumatic experiences. New York: Oxford University Press. Foa, E. B., Riggs, D. S., Dancu, C. V., & Rothbaum, B. O. (1993). Reliability and validity of a brief instrument for assessing post-traumatic stress disorder. Journal of Traumatic Stress, 6(4), 459–473. Foa, E. B., & Tolin, D. F. (2000). Comparison of the PTSD symptoms scale-interview version and the clinician-administered PTSD scale. Journal of Traumatic Stress, 13, 181–191. Foa, E. B., & Williams, M. (2010). Methodology of a randomized double-blind clinical trial for comorbid posttraumatic stress disorder and alcohol dependence. Mental Health and Substance Use, 3, 131–147.

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