Intersectional inequalities in somatic symptom severity: A trans-diagnostic MAIHDA analysis of SOMACROSS data

Persistent somatic symptoms are common and contribute substantially to population health burden. However, the intersectional social patterning of somatic symptom burden remains insufficiently understood. This study examined inequalities in somatic symptom severity across intersections of gender, educational attainment, and migration history. Utilizing a trans-diagnostic patient sample (including the diagnoses primary biliary and primary sclerosing cholangitis, ulcerative colitis, irritable bowel syndrome, chronic kidney disease, pruritus, and somatic symptom disorder; N = 1254) pooled from five research projects of the SOMACROSS research unit, we applied Multilevel Analysis of Individual Heterogeneity and Discriminatory Accuracy (MAIHDA). Gender, history of migration (German-speaking sample), and education were included as indicators of social inequalities. Symptom severity was assessed using the Patient Health Questionnaire 15 (PHQ-15). The sample was predominantly female (62.4%), 81.8% reported no history of migration, and participants were on average 52.2 years old (SD = 16.6). MAIHDA results revealed that social inequalities in somatic symptom severity operate primarily through additive main effects rather than multiplicative interactions. Gender displayed the strongest associations with these inequalities, followed by education, with higher burdens among females and those with lower educational levels, while only weak associations were observed for history of migration. The predominantly additive pattern suggests that interventions targeting individual social determinants may be effective across multiple intersectional groups, supporting a strategy of proportionate universalism. The presence of differences across intersectional strata, irrespective of primary diagnosis, underscores the importance of monitoring health inequalities through an intersectional lens to ensure equitable outcomes.