Psychometric assessment of the Swedish version of the injustice experience questionnaire among patients with chronic pain

Abstract

Objectives The use of the Injustice Experience Questionnaire (IEQ) in psychological assessment of individuals with chronic pain is supported by research. The psychometric properties of the Swedish version, the IEQ-S, has not yet been evaluated. Hence, the aim was to investigate structural validity, and concurrent criterion validity of the IEQ-S against the Work Ability Index (WAI), the Pain Catastrophizing Scale (PCS-SW), the Patient Health Questionnaire 9-item depression module (PHQ-9), and the Generalized anxiety disorder 7-item scale (GAD-7). Internal consistency and test-retest reliability were also studied. Methods Sixty-five participants, referred to a University hospital, with a pain duration over three months were consecutively sampled. They completed the IEQ-S at admission and again within six weeks. A confirmatory factor analysis was performed for the study of structural validity. Concurrent criterion validity was evaluated using Spearman’s correlation coefficient. Internal consistency reliability for the full IEQ-S was calculated using the Cronbach’s alpha. Test-retest reliability was calculated using an Intraclass Correlation Coefficient (ICC). Results The median total score (0–48, where high scores indicate high levels of injustice) at admission (test 1) was 27.0 (n=64), 25th percentile=15.3, 75th percentile=37.8, range=3–48 points. A one-factor model was supported with item-loadings between 0.67–0.92. Spearman’s correlation coefficient between the IEQ-S and the WAI (n=56) was r S =−0.46; the PCS-SW (n=63) was r S =0.68, the PHQ-9 (n=64) was r S =0.50 and the GAD-7 (n=64) was r S =0.57, p<0.01. Cronbach’s alpha was 0.94 (n=64). The ICC was 0.80 (n=55), with a 95% confidence interval, ranging between 0.69–0.88. Conclusions Our study supported structural validity and concurrent criterion validity of the IEQ-S against other measures of psychological constructs and work ability. It also supported the internal consistency reliability of the IEQ-S and the test-retest reliability with a retest interval up to six weeks, was good. These findings support the use of the IEQ-S as an adjunct tool to assess appraisals of injustice in patients with chronic pain who are referred to tertiary care in Sweden. The added value might be identification of those who are at risk for slow or no improvement in their pain condition over time, and sick-leave, but this has to be confirmed in future studies. Ethical committee number EPN Uppsala D-No 2016-376.

Perceived Injustice and Anger in Fibromyalgia with and without Comorbid Mental Health Conditions

“…In the patient groups, the strong correlations between the IEQ and PCS replicate findings both in the IEQ's initial development 7 and more recently (ranging from 0.65 to 0.75). 12,13,15,19,64,66 At the same time, these studies indicated a tendency of the IEQ to explain additional variability above and beyond PCS. In the current study (Supplemental Materials, Supplemental Digital Content 1, http://links.lww.com/ CJP/B83, Tables S1-S3, Supplemental Digital Content 2, http://links.lww.com/CJP/B84, Supplemental Digital Content 3, http://links.lww.com/CJP/B85, Supplemental Digital Content 4, http://links.lww.com/CJP/B86), IEQ scores explained additional pain variability above and beyond PCS only within specific patient groups and pain measures, whereas PCS explained additional variability above and beyond IEQ in only one such case.…”

“…In validating our Hebrew version of the IEQ, we confirmed a 1-factor structure for all 12 items with excellent reliability. Previous validations and translations of the IEQ have yielded mixed results regarding a 2-factor [64][65][66]69 versus 2-factor 19,67,68 structure, although the latter consistently reports very high overlap between the components. As such, our findings support Sullivan et al's 7 original conception that the IEQ might be best construed as a complex but unitary construct, with the theoretical subscales not deriving statistically separate components.…”

“…To test the structural validity, we conducted a factor analysis using Principal Component Analysis (PCA) with oblique (direct oblimin) rotation. Although some validations of the IEQ have employed Confirmatory Factor Analysis, 64,68,69 we opted for PCA in line with the many other IEQ validation studies. 7,19,[65][66][67] Given the varied findings of factor analyses within these papers, we concluded that the more exploratory PCA was preferable to a confirmatory method.…”

“…This sample size is in line with the common ratio for principal component analysis of 10 to 15 participants per questionnaire item 70 and in line with the sample size of previous IEQ validations. 7,14,16,19,64,65,67,69,71 Patient groups were recruited via the Rheumatology Department at Tel Aviv Sourasky Medical Center, and the PFC group were recruited via social media.…”

“…To date, the IEQ has been validated in multiple languages. 19,[64][65][66][67][68][69] We further aimed to translate and validate a Hebrew version of the IEQ, confirming its structure using factor analysis and measuring internal consistency using Cronbach alpha. In line with previous findings, we hypothesized a linear trend such that PI (as measured by the IEQ), state and trait anger, and measures of anxiety, depression, and pain catastrophizing will be greater in FM+A/D compared with FM-A/D, RA, and PFCs, respectively.…”