Exploring the properties of the Intersectional Discrimination Index — Major in Canadian Veterans with chronic pain

LAY SUMMARY In this study, the utility of a new self-report scale to capture experiences of discrimination or violence among a sample of Canadian military Veterans with chronic pain was evaluated. The Intersectional Discrimination Index — Major (InDI-M) was administered through an online survey along with other scales to measure experiences of pain, mood disorder, and functional interference. Results indicate that the InDI-M appears to measure both experiences of interpersonal violence and of systemic inequity, although some problems were identified when using the scale in this sample of predominantly white male Veterans. The InDI-M might be a useful research tool for exploring effects of interpersonal violence on pain and mental health but less so for exploring experiences of systemic inequity in military Veteran health research. Introduction: Social determinants of pain have been difficult to study because few measurement scales exist. The Intersectional Discrimination Index — Major (InDI-M) is a new, 13-item scale with potential for use in pain research, though little is known about its utility across different populations. This study evaluates the measurement properties of the InDI-M among Canadian military Veterans with chronic pain. Methods: Data were collected through an online survey that included the InDI-M and questions related to pain, depression, anxiety, and intersectional identities. Results: Factor analysis converged on a 10-item, two-factor structure for the InDI-M. The factors were termed Systemic Inequity (four items; α = 0.68) and Interpersonal Violence (six items; α = 0.78). The pattern of concurrent associations with external criteria revealed meaningful effects of presence of mental health disorder (Interpersonal Violence subscale scores higher among those with depression [6.3/12] or anxiety [6.3/12] than among those without [5.0/12 and 5.1/12, respectively; p < 0.05) but only one significant association with a pain metric (Systemic Inequity with pain interference; r = 0.11, p < 0.05). The Interpersonal Violence subscale showed stronger properties than the Systemic Inequity subscale. The sample was predominantly white and male, reducing response distribution. Discussion: The InDI-M appears to be more useful for capturing experiences of interpersonal violence among military Veterans and less so for inequity and marginalization, and it may hold value for pain research. It may capture intersectional discrimination or negative experiences during military service among this population. Suggestions for future research directions are provided.