A total of 274 subjects were recruited from 8 medical institutions throughout Korea, from February 2016 until March 2017. The 274 study subjects comprised 71 with PTSD, 74 with mood disorder or anxiety disorder as a psychiatric control group, and 99 as a healthy control group. PTSD and other psychiatric disorders were diagnosed by the structured clinical interview for DSM-5-research version (SCID-5-RV).11 The SCID-5-RV is a semi-structured interview guide for making DSM-5 diagnoses, including depression, anxiety, and PTSD. Interviewer training consisted of lectures on the SCID-5-RV and related questionnaires, observation of an evaluation performed by an experienced psychiatrist, and group evaluation of videos of PTSD patients. The diagnoses of subjects in the psychiatric control included major depressive disorder (n = 44), panic disorder (n = 6), and generalized anxiety disorder (n = 24). The healthy control group included 88 randomly selected individuals visiting the institutions for regular health screening. All the healthy controls demonstrated that they did not have a lifetime history of psychiatric disorders in SCID-5-RV.

Exclusion criteria for psychiatric disorders were being younger than 18 or older than 70 years, having been diagnosed with a present or past diagnosis of psychotic disorders, and were not able to complete the CAPS-5 interview. To assess test-retest reliability, only the PTSD patients with stable PTSD symptoms and who agreed to a second K-CAPS-5 assessment were included.

After obtaining permission from the National Center for PTSD, three bilingual psychiatrists and one psychologist in English and Korean initially translated CAPS-5; this was followed by a process of back translation and revisions. Two other bilingual Korean psychiatrists and one psychologist performed the back translation blindly. Finally, a translation committee, which consisted of five Korean psychiatrists, one Korean language and literature professor, and one psychologist, made the final version of K-CAPS-5.

The Korean version of SCID-5-RV (K-SCID-RV) was used to assess the convergent validity of K-CAPS-5. We used SCID-RV as the gold standard assessment of DSM-5 PTSD. SCID-5-RV is a semi-structured interview guide for making DSM-5 diagnoses for depression, anxiety and PTSD. It was administered by trained mental health professionals that were familiar with the DSM-5 classification and diagnostic criteria.

The Beck Depression Inventory-II (BDI-II),12 the Beck Anxiety Inventory (BAI),13 the Impact of Event Scale-Revised (IES-R),14 and the Spielberger State Trait Anxiety Inventory (STAI)15 were also performed to assess the correlations with the scores of K-CAPS-5. BDI-II, a 21-item self-administered questionnaire, was designed to evaluate the severity of depression, and BAI with 21 items for evaluating the severity of anxiety. IES-R, a 22-item self-reporting questionnaire composed 8 questions for intrusion, 8 for avoidance, and 6 for hyperarousal, was used to assess the severity of PTSD symptoms. STAI, with 40 self-check questions, was developed to assess the severity of state anxiety and trait anxiety. The Korean versions of BDI, BAI, IES-R and STAI have previously been shown to exhibit excellent psychometric properties, and their internal consistency coefficients were reported to be 0.85,16 0.90,17 0.76,18 and 0.91,19 respectively.

The 8 interviewers in this study were skilled board-certificated psychiatrists and clinical psychologists with careers in PTSD practice of at least five years. The consensus meeting consisted of lecturing on K-CAPS-5 and related questionnaire characteristics, observing the evaluation by an experienced psychiatrist, and evaluating the video-recorded PTSD patients together. The inter-rater reliability values of the PTSD module of SCID-RV and K-CAPS-5 were high, with intra-class correlation coefficients of 0.74 and 0.80, respectively.

Among the PTSD, psychiatric control, and normal control groups, demographic variables and clinical characteristics were compared using the analysis of variance (ANOVA) and χ² analyses to compare the quantitative and categorical variables. In order to measure the internal consistencies of K-CAPS-5, Cronbach's alpha coefficients were computed, and the item-total correlation coefficients of these scales were measured to confirm that all the items on these scales also exhibited internal consistency. Test-retest reliability and the inter-rater reliability were calculated by means of the intraclass correlation coefficients. Test-retest reliability was evaluated by the same interviewers who performed the two testing sessions within 5 days. To measure the agreement of each item between K-CAPS-5 and SCID-5-RV, Pearson's χ² and Cohen's κ coefficient were calculated. Cohen's κ coefficient ranges from 0 to 1; values of 0.8 and over are considered to indicate ‘good agreement’ and values of 0.6–0.8 are considered to indicate substantial agreement.20 Pearson correlation coefficients were used to evaluate the concurrent validity between K-CAPS-5, BDI-II, BAI, IES-R, and STAI. ANOVA with Tukey's post hoc test was performed to evaluate the between-group difference by the severity measured by K-CAPS-5. An exploratory factor analysis was performed using principal component analysis with varimax rotation to determine the factor structure of K-CAPS-5. The optimal cutoff scores of K-CAPS-5 that best predicted current PTSD by SCID-5-RV were estimated by receiver operating characteristics curve analysis. The sensitivities, specificities, positive predictive values, negative predictive values, and κ values were measured for each threshold score of K-CAPS-5.

Analyses were performed using SPSS version 18.0 (SPSS, Chicago, IL, USA). Statistical significance was set at P < 0.05.

This study was approved by the public Institutional Review Board of the Ministry of Health and Welfare of Korea (P01-201508-21-002). All subjects were informed of the study purpose and methods and provided written informed consent.

The mean ages of the PTSD, psychiatric control, and normal control groups were 46.9 (standard deviation [SD], 14.3), 43.7 (SD, 12.1), and 44.6 (SD, 9.2) years, respectively. The numbers of males in the three groups were 42 (60.0%), 34 (45.9%), and 37 (37.4%), respectively. No significant differences were found for age (F = 1.433, P = 0.241), although a significant difference in gender ratio was found among the three groups (χ² = 8.452, P = 0.015). There was no significant difference in marital status among the three groups. The mean duration of symptoms in the PTSD group was 22.31 (SD, 29.17; range, 1.10–126.67) months. The worst traumas experienced in the PTSD group were serious accidents, such as automobile or man-made disasters (n = 51, 72.9%), physical assault (n = 7, 10.0%), sexual abuse (n = 6, 28.6%), combat experience (n = 2, 2.9%), life-threating medical disease (n = 2, 2.9%), and witnessing an accident (n = 2, 2.9%).

Cronbach's α was used to evaluate the internal consistency of K-CAPS-5 in the 71 PTSD patients. Internal consistency for the K-CAPS-5 total score was 0.92 at baseline. Alpha coefficients for intrusion, avoidance, cognition/mood, and arousal/reactivity were 0.83, 0.71, 0.82, and 0.75, respectively. Based on the criterion of 0.30 as an acceptable corrected item-total correlation,19 all 20 items performed adequately (range, 0.38–0.79) (Table 1).

Among the 71 PTSD subjects, 34 were recruited for the evaluation of the test-retest reliability. The test-retest reliability was determined to be 0.91 (P < 0.001).

The total scores ± standard error (SE) of K-CAPS-5 in the PTSD group, the psychiatric controls and normal controls were 33.03 ± 1.07, 18.00 ± 9.79, and 6.18 ± 5.86, respectively. These values were significantly different by ANOVA (overall F = 115.87, P < 0.001). The Tukey's post-hoc test showed that there were significant differences among the three groups. These results showed the good construct validity of K-CAPS-5.

Table 2 shows the value of Pearson's χ² and Cohen's κ coefficient between K-CAPS-5 and SCID-5. Both PTSD diagnosis (κ = 0.893) and dissociative subtype of PTSD were in almost perfect agreement (κ = 0.839). According to the detailed diagnosis criteria, Cohen's κ coefficient of traumatic experience was 0.705, which corresponds to substantial agreement, and Cohen's κ coefficients of intrusion, avoidance, cognition/mood, and arousal/reactivity were all more than 0.910, which were in almost perfect agreement.

The total K-CAPS-5 score was correlated with BDI (r = 0.58, P < 0.001), BAI (r = 0.67, P < 0.001), IES-R (r = 0.78, P < 0.001), and STAI-T (r = 0.37, P = 0.003). Thus, the correlation of K-CAPS-5 was strong with IES-R, relatively weak with STAI-T, and intermediated with BDI-II (Table 3).

The explorative factor analysis with varimax rotation on the items of K-CAPS-5 for the 71 subjects from the PTSD group yielded six factors that explained the results and which together accounted for 61.91% of the variance (Table 4). Given the contents, the first factor, which consisted of six items (D5 [diminished interest], D6 [detachment from others], D4 [negative emotional state], D7 [no positive emotions], D2 [negative belief], and D3 [distorted blame]), could be interpreted as a dimension of “negative affect in cognition and moods” (eigenvalue, 2.54; percentage of variance, 12.72%). Similarly, the second factor covered five items (B3 [flashbacks], B5 [cued physiological reaction], B4 [cued psychological], B1 [intrusive memory], and D1 [dissociative amnesia]) and was related to “intrusion” (eigenvalue, 2.48; percentage of variance, 12.42%). The third factor consisted of four items (E5 [poor concentration], E1 [irritability/aggression], E2 [reckless/self-destructive], and E4 [exaggerated startle response]) and was related to “alteration in reactivity” (eigenvalue, 2.20; percentage of variance, 10.98%). The fourth factor consisted of two items (C2 [avoidance of external reminders] and C1 [avoidance of memories]) and was related to “avoidance” (eigenvalue, 1.76; percentage of variance, 8.82%). The fifth factor consisted of two items (E6 [sleep disturbance] and B2 [distressing dreams]), and was loaded on “sleep disturbance” (eigenvalue, 1.70; percentage of variance, 8.50%). The sixth factor consisted of one item (E3 [hypervigilance]) and was loaded on “hyperarousal” (eigenvalue, 1.69; percentage of variance, 8.47%).