Persistent somatic symptoms (PSS) are more prevalent among individuals with low socioeconomic status (SES) and migration background, but the factors explaining these social inequalities remain largely unclear. PSS conditions such as irritable bowel syndrome (IBS, approximately 10–20% prevalence in Germany) and fatigue (approximately 30% prevalence in Germany) are highly common, yet research on social inequalities in these conditions—particularly in Germany—is scarce. Existing studies give inconsistent results. For example, Jason et al. found highest fatigue levels among minority groups and those with lower education in the USA, while German data show mixed findings for IBS (some studies find higher prevalence in lower SES groups, others find no association or a reverse pattern). Aetiological models suggest that psychosocial maintaining or aggravating factors—including health anxiety, illness beliefs, illness perception, and illness behaviour—may partially mediate social inequalities in PSS. Limited health literacy has been documented among low SES and migrant populations, and a study comparing German and Turkish somatoform disorder patients found Turkish patients believed significantly more strongly in supernatural causes of their disease, which reduced motivation to engage in psychotherapy. A recent meta-analysis showed a lower risk for health anxiety in people with higher SES, while another meta-analysis indicated higher health anxiety risk in migrants and ethnic minorities in North America. SOMA.SOC was designed to fill this knowledge gap and is part of the interdisciplinary SOMACROSS research unit (FOR 5211), which proposes a biopsychosocial 'PSS working model' as the starting framework.
SOMA.SOC employs a mixed-methods observational design with two complementary parts. The first is a cross-sectional population survey conducted throughout Germany via computer-assisted telephone interviewing, with a planned sample of N=2400 adults aged 18 years and older. A dual-frame approach is used (30% mobile, 70% landline), and participants are randomly selected using the Kish-Selection-Grid. Data are weighted by household size, selection probabilities, and socio-demographic distributions for representativeness. Sixteen vignettes are randomly assigned (n=150 per vignette), varying condition (IBS/fatigue), sex (male/female), occupational status (high [lawyer]/low [cleaner]), and migration history (yes/no). The sample size of n=150 per vignette enables detection of small effect sizes (χ² tests, t-tests, ANOVA) with 80% power and α=0.05, based on similar prior vignette studies with response rates of 48–54%.
The second part consists of longitudinal qualitative semi-structured interviews with N=32 patients recruited from approximately 25 primary care practices in Hamburg (out of 50 randomly selected from about 3000 practices). Inclusion criteria rely on ICD-10 codes K58.1, K58.2, K58.3, K58.8, R53, F48.0, and G93.3. Purposeful sampling ensures two patients per 16-stratum combination (condition × sex × occupational status × migration). Each patient is interviewed at three time points (t0, 6 months [t1], 12 months [t2]), yielding 96 interviews in total. Interviews last approximately 30 minutes and cover three sections: origin/causes/development of disease; coping and help-seeking; and social interaction and perception by others. Each patient receives €15 per interview (€45 total); physicians receive €50 per included patient.
The survey questionnaire covers health literacy (including Illness Perception Questionnaire brief version), illness beliefs, public stigma and anticipated stigma (modified IBS Stigma Scale), illness behaviour, healthcare usage, somatic symptom burden (Somatic Symptom Scale-8), health anxiety (Whiteley Index-7), illness experience, and socio-demographics including educational attainment, occupational position, monthly equivalence household income, and migration status (no migration background, first- and second-generation migrants per the German Federal Statistical Office definition). Approximately 600 of the 2400 respondents are expected to have a migration background (matching the ~25% German population rate).
For the survey, regression models test associations between respondents' social characteristics and aggravating factors (hypothesis 1). Structural equation modelling explores mediation of PSS inequalities by aggravating factors. Differences in public perceptions according to migration and occupational status of the vignette person (hypothesis 2) are examined via ANOVA, χ² tests, and interaction tests. Missing data are imputed if >5% missing. Qualitative interviews undergo audio recording, transcription, and qualitative content analysis using inductive category formation. Findings from both study parts are integrated via a 'convergence coding matrix' at the interpretation stage.
**Clinical Implications**
Given that this is a study protocol, no results are yet available. Expected deliverables include identification of disease-specific and overarching mechanisms through which SES and migration shape PSS persistence via health literacy, stigma, illness perception, illness behaviour, and health anxiety. Such findings could inform targeted interventions addressing health literacy gaps and stigma in vulnerable populations, potentially reducing disparities in IBS and fatigue outcomes. The two-perspective design (public and patient views) is intended to provide a comprehensive understanding of how social characteristics contribute to symptom persistence, supporting the development of more equitable healthcare strategies within the broader SOMACROSS framework.
**Ethics and Dissemination**
The Ethics Committee of the Hamburg Medical Association approved the protocol on 25 January 2021 (reference 2020-10194-BO-ff). Data collection runs April 2022 to summer 2024. De-identified quantitative data will be made publicly available per FAIR Data Principles. Main findings will be submitted for publication within 12 months of study completion.