Test-Retest Reliability and Construct Validity of the Dutch Injustice Experience Questionnaire in Patients with Chronic Pain

Perceived injustice is defined as an appraisal of the severity of loss, blame, a sense of unfairness, and irreparability of loss related to pain. It has a negative impact on health and is associated with poor recovery outcomes in pain rehabilitation programs. In order to measure, the Injustice Experience Questionnaire (IEQ) was developed, but the reliability and validity of the Dutch version of the IEQ had not been studied. This study aimed to investigate construct validity and test-retest reliability of the Dutch IEQ. Included patients were 281 adults with multi-factorial chronic pain (> 3 months) from two health care settings. All patients filled out questionnaires that measured perceived injustice, pain characteristics, central sensitization, disability, pain catastrophizing, pain acceptance, depression, anxiety, PTSD symptoms, anger, and perceived illness threat. Thirteen hypotheses on the strength of the correlations between the IEQ and the other measurements were formulated a priori. Correlations were calculated using Pearson correlation coefficients. To evaluate test-retest reliability, the IEQ was assessed 2 weeks later and intra-class correlations were computed. All measurements, apart from pain duration and number of pain sites, were significantly correlated with the IEQ. Eleven out of 13 hypotheses were confirmed. Intra-class correlation between the first and second assessments of the IEQ was 0.87. The results support the construct validity of the Dutch IEQ and suggest that test-retest reliability is good.