Developing a Japanese version of the Injustice Experience Questionnaire-chronic and the contribution of perceived injustice to severity of menstrual pain: a web-based cross-sectional study

BACKGROUND: Menstrual pain causes low quality of life among women of reproductive age, and often interferes with daily activities. Perceived injustice is a cognition linked to adverse symptoms. The aims of this study were to develop a Japanese version of the Injustice Experience Questionnaire-chronic (IEQ-chr-J), and to examine if perceived injustice is associated with pain intensity and impairment from menstruation. METHODS: We investigated 130 Japanese women (aged 20–45 years) with menstrual pain in the past 3 months using online self-administered questionnaires. We examined the psychometric properties of the IEQ-chr-J including: structural validity; internal consistency; and test-retest reliability (intra-class correlation coefficients; ICC). Concurrent validity was examined by correlations among the IEQ-chr-J, the Pain Catastrophizing Scale (PCS), the Hospital Anxiety and Depression Scale (HADS), a numerical rating scale (NRS) for maximum/average menstrual pain, and the Brief Pain Inventory (BPI) pain interference domain. We used multivariable regression analysis to investigate the association between perceived injustice and severity of menstrual pain, after excluding 10 hormone drug users. RESULTS: The IEQ-chr-J showed sufficient validity and reliability (Cronbach’s α = 0.96, ICC 0.75, [95% confidence interval (CI): 0.61–0.88]. Pearson’s correlation coefficients for the IEQ-chr-J, PCS, HADS anxiety, HADS depression, NRS, and BPI pain interference ranged from 0.27–0.65. The IEQ-chr-J was correlated with impairment due to menstrual pain (ICC 0.36, 95% CI: 0.14–0.58), an independent diagnosis of endometriosis, anxiety, and depression, but not with maximum or average pain intensity. CONCLUSIONS: The IEQ-chr-J has acceptable psychometric properties, and perceived injustice is associated with impairment from menstrual pain. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13030-019-0158-z) contains supplementary material, which is available to authorized users.