Characteristics of the participants
Participants in this study (N = 214, mean age = 33.1±12.4 years) were women complaining from CPP. The participants experienced several types of pain (stabbing pelvic pain, sex pain, bowel pain, and headache), somatic symptoms (e.g., bloating, nausea, dizziness, unusual sweating), along with symptoms of low mood, anxiety, and psychiatric comorbidity. Table 1 shows more information on the sociodemographic and clinical characteristics of the participants in the overall sample as well as group differences in these variables between low distress and high distress women.
Results of confirmatory factor analysis and invariance analysis
As shown in Table 2, the one-factor structure of the DASS-8/DASS-12 expressed unsatisfactory fit. The crude models of the three-factor structures of the DASS-8 and the DASS-12 expressed good fit. Correlating the error terms of two items (Figure 1) in both models slightly improved the fit. The fit of the second order structure was similar to that of the three-factor structure of both scales (supplementary material). While the bifactor structure of the DASS-8 expressed good fit with all items significantly loading on the general factor, item 12 and item 20 failed to load on their domain-specific factors of stress and anxiety, respectively (p >.05). In addition, item 15 loaded significantly on the anxiety factor (p = .04), but its loading on this factor was weak (β = .26). All items of the anxiety subscale of the DASS-12 failed to load on their corresponding factor in the bifactor model. Therefore, the three-factor structures of the DASS-8/DASS-12 represent the best fit of the data.
As shown in Table 3, the three-factor structures of the DASS-8 and DASS-12 were invariant at the configural, metric, scalar, and strict levels across groups of age and menopausal status. However, the DASS-8 was non-invariant at the scalar level across groups of psychiatric comorbidity (ΔCFI > 0.02 and ΔRMSEA >0.15). The DASS-12 was non-invariant at the strict level (ΔCFI > 0.02 and ΔRMSEA >0.15), and it also tended to be non-invariant at the scalar level across comorbidity groups (SRMR = 0.1117).
Results of discriminant validity tests
As noted in Table 4, the DASS-21, DASS-8, DASS-12 differentiated between women with a current psychiatric disorder and those without at the same level of significance (p < 0.001). However, the z scores of the DASS-8 and its subscales were higher than those of the DASS-12 and the DASS-21, indicating a higher level of discriminant validity. Nonetheless, neither the DASS-21, DASS-8, DASS-12 nor their subscales could differentiate women with a diagnosis of depression from those with a diagnosis of anxiety. Likewise, the DASS-21, DASS-8, DASS-12, and their subscales significantly correlated with subjective experience of anxiety and low mood at the same levels (all p values < 0.01, Table 4). The HTMT ratio of correlations show that the constructs covered by the subscales of the DASS-8 and DASS-12 were distinct (< 0.85). However, the stress and anxiety subscales on the DASS-8 were overlapping (HTMT ratio = 0.95). All the subscales of the parent scale exhibited overlap, albeit it was marginal for the stress-anxiety subscales (HTMT ratio = 0.85 supplementary materials).
Table 4
Descriptive statistics and discriminant validity of the Depression Anxiety Stress Scale 21 and its shortened versions among women with chronic pelvic pain
DASS versions | Whole sample (N = 214) | Mann Whitney test | z | Cluster 1 (n = 141) | Cluster 2 (n = 73) | Mann Whitney test | z |
MD (IQR) | MD (IQR) | MD (IQR) |
DASS-21 | 11.5 (6.0-23.8) | 2247.5 | -5.49 | 7.0 (4.0-11.8) | 29.5 (23.0-36.8) | 210.0 | -11.43 |
Depression | 2.0 (1.0-7.0) | 2495.5 | -5.08 | 1.0 (0-3.0) | 9.0 (5.0-14.0) | 1041.0 | -9.65 |
Anxiety | 3.0 (1.0-7.0) | 2482.0 | -5.11 | 1.0 (0-3.0) | 8.0 (6.0-11.0) | 728.0 | -10.39 |
Stress | 6.0 (3.0-11.0) | 2641.0 | -4.48 | 4.0 (2.0-6.0) | 12.0 (10.0-16.0) | 436.5 | -10.91 |
DASS-12 | 7.0 (3.0-13.3) | 2320.0 | -5.48 | 4.0 (2.0-7.0) | 17.0 (13.0-21.0) | 397.0 | -11.08 |
Depression | 1.0 (1.0-4.0) | 2266.5 | -5.80 | 0 (0-1.0) | 5.0 (3.0-8.5) | 1082.0 | -9.77 |
Anxiety | 2.0 (0-4.0) | 2842.0 | -4.24 | 1.0 (0-2.0) | 4.0 (3.0-6.0) | 1514.5 | -8.63 |
Stress | 4.0 (2.0-7.0) | 2849.5 | -4.16 | 2.0 (1.0-4.0) | 8.0 (6.0-9.5) | 856.0 | -10.05 |
DASS-8 | 4.0 (1.0-8.0) | 2018.0 | -6.27 | 2.0 (1.0-3.0) | 12.0 (8.0-15.0) | 36.0 | -11.95 |
Depression | 1.0 (0-3.0) | 2346.5 | -5.60 | 0 (0-1.0) | 4.0 (2.0-6.0) | 1214.0 | -9.47 |
Anxiety | 1.0 (0-3.0) | 2521.0 | -5.21 | 0 (0-1.0) | 4.0 (3.0-6.0) | 674.0 | -10.93 |
Stress | 2.0 (1.0-3.0) | 2447.0 | -5.26 | 1.0 (0-2.0) | 4.0 (3.0-5.0) | 364.0 | -11.37 |
DASS: Depression Anxiety Stress Scale, MD: median, IQR: interquartile range, U: Mann Whitney U test, p values were all significant at 0.001 level. For the DASS-21 (N = 212). |
In two-step cluster analysis, the DASS-8 and its subscales classified the participants into two clusters: low distress (cluster 1: n = 141, 65.9%) and high distress (cluster 2: n = 73, 34.1%). The model expressed good fit as indicated by Silhouette measure of cohesion and separation of around 0.7 and ratio of sizes less than 3 (1.93). Values of the predictor importance of the DASS-8 followed by stress, anxiety, and depression were 1, 0.85, 0.73, and 0.5, respectively. Mann Whitney U test revealed significant differences in the level of all mental distress symptoms among participants in both clusters—they were all significantly higher in cluster 2 than in cluster 1 (all p < 0.001), with the DASS-8 and its stress subscale expressing the highest z scores (Table 4).
Age, menopausal status, bloating, and the frequency of stabbing pelvic pain and sex pain did not vary significantly across clusters. However, participants in cluster 2 demonstrated significantly higher number of pain days (t(146.9)= -2.50, p = 0.014), less pain free days (U = 3654.0, z = -2.39, p = 0.017); more severity of stabbing pelvic pain (t(134.42) = -2.47, p = 0.015), sex pain (t(105.22) = -3.74, p = 0.001), current pelvic pain (U = 3095.0, z = -3.29, p = 0.001), concurrent headache (t(118.11) = -3.51, p = 0.001); higher frequency of bowel pain (χ 2(1) = 6.68, p = .010), greater occurrence of sexual assault (χ 2(1) = 19.06, p = .001), psychiatric co-morbidity (χ 2(2) = 23.61, p = 0.001), psychiatric symptoms (low mood (χ2(16) = 29.8, p = 0.001) and anxiety (χ 2(1) = 50.50, p = 0.001)), fatigue (χ 2(1) = 14.12, p = 0.001), sleep problems (χ 2(16) = 12.13, p = 0.001), and somatic symptoms (dizziness (χ 2(1) = 7.57, p = 0.006), unusual sweating (χ 2(1) = 9.52, p = 0.002), and nausea (χ 2(1) = 13.65, p = 0.001)).
Results of tests of reliability, normality, and criterion validity
The reliability of the DASS-21, DASS-8, and DASS-12 was excellent. Meanwhile, the reliability of the shortened subscales ranged from very good to poor (Table 5)—poor reliability was reported only for the anxiety subscale of the DASS-12. The predictive validity of the DASS-8, DASS-12, and their subscales is depicted by their strong correlation with the original scale and its subscales (Table 5). The normality of the DASS-8 and the DASS-12 is comparable with that of the DASS-21 as noted by Shapiro–Wilks’ W. As shown in Table 5, all the DASS versions and most of their subscales negatively correlated with pain-free days and positively correlated with pain experience on the survey day, pain days per month, concurrent headache, poor sleep, fatigue, somatic symptoms (nausea, bloating, dizziness, unusual sweating), experience of low mood and anxiety, as well as sexual assault experience. Notably, all the subscales of the DASS-8 correlated with sexual assault experience while the anxiety and stress subscales of the DASS-12 as well as the stress subscale of the DASS-21 could not correlate with this variable. Similarly, all subscales of the DASS-8 correlated with the severity of stabbing pelvic pain while the stress subscale of the DASS-12 and the DASS-21 failed to correlate with this variable.
Table 5
Internal consistency, predictive validity, normality, and criterion validity of the Depression Anxiety Stress Scale (DASS) 21, DASS-12, DASS-8, and their subscales among women with chronic pelvic pain
Criteria | DASS-21 | Depression | Anxiety | Stress | DASS-12 | Depression | Anxiety | Stress | DASS-8 | Depression | Anxiety | Stress |
Coefficient alpha | 0.945 | 0.931 | 0.837 | 0.878 | 0.898 | 0.845 | 0.693 | 0.827 | 0.901 | 0.892 | 0.794 | 0.705 |
Range of corrected item-total correlations | 0.401-0.776 | 0.598-0.847 | 0.370-0.713 | 0.593-0.735 | 0.401-0.785 | 0.607-0.719 | 0.371-0.550 | 0.607-0.746 | 0.629-0.744 | 0.882-0.944 | 0.634-0.662 | 0.545 |
Range of alpha if-item-deleted | 0.940-0.946 | 0.914-0.939 | 0.795-0.853 | 0.851-0.869 | 0.881-0.902 | 0.787-0.833 | 0.585-0.708 | 0.742-0.809 | 0.884-0.893 | 0.831-0.870 | 0.702-0.733 | -- |
Correlation with subscale of the DASS-21 | -- | -- | -- | -- | -- | 0.930*** | 0.919*** | 0.948*** | -- | 0.934*** | 0.871*** | 0.871*** |
Correlation with the DASS-21 | -- | 0.856*** | 0.823*** | 0.929*** | 0.966*** | 0.838*** | 0.718*** | 0.863*** | 0.943*** | 0.811*** | 0.789*** | 0.818*** |
Shapiro Wilk test | 0.892*** | 0.812*** | 0.848*** | 0.936*** | 0.906*** | 0.787*** | 0.843*** | 0.933*** | 0.864*** | 0.788*** | 0.790*** | 0.891*** |
Correlation with sexual assault experience | 0.203** | 0.264*** | 0.196** | 0.134 | 0.192* | 0.278*** | 0.095 | 0.106 | 0.259** | 0.245** | 0.261*** | .188* |
Correlation with pain days/month | 0.183** | 0.137 | 0.221** | 0.183** | 0.193** | 0.190** | 0.204** | 0.136 | 0.180* | 0.177* | 0.172* | .163* |
Correlation with pain-free days/month | -0.182** | -0.132 | -0.217** | -0.174* | -0.193** | -0.188** | 0-.201** | -0.139* | -0.179* | -0.173* | -0.168* | -.168* |
Correlation with severity of pain today | 0.265*** | 0.217** | 0.331*** | 0.238** | 0.290*** | 0.255*** | 0.291*** | 0.239** | 0.265*** | 0.225** | 0.274*** | .234** |
Correlation with severity of stabbing pelvic pain | 0.200** | 0.167* | 0.287** | 0.138 | 0.209** | 0.174* | 0.246** | 0.143 | 0.205** | 0.149* | 0.246** | .153* |
Correlation with severity of pain during sexual activity | 0.262** | 0.308*** | 0.210* | 0.222** | 0.280** | 0.326*** | 0.187* | 0.229** | 0.257** | 0.285** | 0.218** | .227** |
Correlation with severity of bad headache | 0.387*** | 0.300** | 0.253** | 0.378*** | 0.395*** | 0.324*** | 0.221* | 0.363*** | 0.299** | 0.303** | 0.225* | .234** |
Correlation with experienced anxiety | 0.517** | 0.430** | 0.412** | 0.491** | 0.498** | 0.427** | 0.323** | 0.478** | 0.531** | 0.425** | 0.473** | .467** |
Correlation with experienced low mood | 0.487** | 0.482** | 0.323** | 0.446** | 0.478** | 0.512** | 0.227** | 0.447** | 0.514** | 0.492** | 0.400** | .412** |
Correlation with experienced fatigue | 0.345** | 0.296** | 0.333** | 0.305** | 0.348** | 0.300** | 0.346** | 0.288** | 0.322** | 0.283** | 0.231** | .298** |
Correlation with poor sleep | 0.303** | 0.250** | 0.337** | 0.248** | 0.305** | 0.227** | 0.329** | 0.238** | 0.283** | 0.246** | 0.240** | .257** |
Correlation with dizziness | 0.251** | 0.174** | 0.333** | 0.191** | 0.243** | 0.192** | 0.335** | 0.150* | 0.244** | 0.181** | 0.262** | .211** |
Correlation with unusual sweating | 0.238** | 0.182** | 0.280** | 0.215** | 0.239** | 0.174* | 0.306** | 0.197** | 0.222** | 0.179** | 0.189** | .257** |
Correlation with nausea | 0.256** | 0.240** | 0.339** | 0.180* | 0.259** | 0.221** | 0.349** | 0.145* | 0.236** | 0.219** | 0.260** | .154* |
Correlation with bloating | 0.259** | 0.216** | 0.255** | 0.206** | 0.247** | 0.213** | 0.234** | 0.193** | 0.279** | 0.245** | 0.234** | .246** |
*, **, ***: correlation is significant at a level of 0.05, 0.01, 0.001, respectively. |
After trimming non-significant paths, SEM used to test criterion validity of the DASS-8/DASS-12 expressed good fit (χ2(16, 16) = 10.677, 6.956; p = 0.829, 0.974; both CFI= 1.00, both TLI = 1.00, both RMSEA = 0.00, SRMR = 0.0420, 0.0376). Scores of the DASS-8/DASS-12 significantly predicted current pain severity, poor sleep, and sex pain. Scores of their anxiety subscales predicted concurrent headache while scores of their stress subscales predicted the number of pain days per month (Figure 2). The DASS-8 and DASS-12 exerted significant indirect effects on headache through current pain severity (β = -0.055, 95% CI: -0.120 to -0.011, p = 0.023) and (β = -0.067, 95% CI: -0.142 to -0.018, p = 0.011), respectively as well as on sex pain through poor sleep (β = 0.070, 95% CI: 0.023 to 0.114, p = 0.011) and (β = 0.073, 95% CI: 0.031 to 0.118, p = 0.011, 0.007), respectively. Month pain days mediated the effect of the stress subscale of the DASS-8 and DASS-12 on sex pain (β = -0.045, 95% CI: -0.091 to -0.007, p = 0.037) and (β = -0.042; 95% CI: -0.100 to -0.009; p = 0.041), respectively.