Longitudinal evaluation of the psychometric stability of the somatic symptom scale-8 (SSS-8) in a large German general population sample

www.nature.com/scientificreports OPEN Longitudinal evaluation of the psychometric stability of the somatic symptom scale-8 (SSS8) in a large German general population sample Julia Petersen1, Elmar Brähler1,2, Nora Hettich-Damm1, Rieke Baumkötter3,4, Philipp S. Wild3,4,5,6, Alica Hartmann7, Karl J. Lackner8, Jochem König9 & Manfred E. Beutel1 The Somatic Symptom Scale (SSS-8) is a brief 8-item tool for screening common somatic symptoms. This study is the first to examine its temporal invariance and stability across three COVID-19 pandemic time points, while also analyzing changes in SSS-8 scores in the general population and across groups (sex, age, relationship status, poverty status), and testing temporal stability and measurement invariance. Longitudinal data from three pandemic time points in a large population-based sample were used. Temporal stability was assessed using Pearson correlations, and confirmatory factor analysis with measurement invariance testing examined factor validity and temporal invariance. The SSS-8 decreased from the first to the second measurement and subsequently increased between the second and third time points. The scale demonstrated good internal consistency (α ≥ 0.78, ω ≥ 0.82) and temporal stability, with test–retest coefficients ranging from 0.696 to 0.752. Across groups, female sex, age under 60, being not at-risk-of-poverty, and no necessary medical visits during the pandemic were consistently associated with lower test–retest coefficients than their counterparts. Confirmatory factor analysis showed good model fit (CFI = 0.985, TLI = 0.975, RMSEA = 0.040, SRMR = 0.035), and measurement invariance across time points was established (ΔCFI < 0.010). Consistent with other studies, somatic symptom burdening initially decreased and subsequently increased at the third measurement time point. The increase is discussed in the context of the pandemic and the serious political crisis in 2022. Overall, the scale demonstrated good psychometric properties including sensitivity to major crises of life conditions. Keywords Somatic Symptom Scale, psychometrics, confirmatory factor analysis, measurement invariance, SARS-CoV-2 Somatic symptoms are reported frequently among the general population and represent more than isolated physical complaints. Prior research indicated that a higher somatic symptom load is closely linked to mental health burden, increased health care utilization, and reduced quality of life, suggesting that somatic symptoms function as an important marker of overall psychosocial vulnerability1,2. Somatic symptoms have characteristically been 1Department of Psychosomatic Medicine and Psychotherapy, University Medical Center of the Johannes Gutenberg- University Mainz, Zahlbacher Straße 8, 55131 Mainz, Germany. 2Clinic and Polyclinic for Psychosomatic Medicine and Psychotherapy, Rostock University Medical Center, Rostock, Germany. 3Preventive Cardiology and Preventive Medicine, Center for Cardiology, University Medical Center of the Johannes Gutenberg-University Mainz, Mainz, Germany. 4Partner Site Rhine Main, German Center for Cardiovascular Research (DZHK), University Medical Center of the Johannes Gutenberg-University Mainz, Mainz, Germany. 5Center for Thrombosis and Hemostasis (CTH), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany. 6Institute of Molecular Biology (IMB), Mainz, Germany. 7Department of Ophthalmology, University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany. 8Institute of Clinical Chemistry and Laboratory Medicine, University Medical Center of the Johannes Gutenberg-University Mainz, Mainz, Germany. 9Institute of Medical Biostatistics, Epidemiology and Informatics, University Medical Center of the Johannes Gutenberg-University Mainz, Mainz, Germany. email: Scientific Reports | (2026) 16:15872 | https://doi.org/10.1038/s41598-026-51808-0 1 found in respondents with various medical conditions such as cancer or coronary heart disease3,4. Populationbased studies further demonstrated that women and older adults consistently report higher somatic symptom loads, highlighting stable demographic gradients that persist beyond specific clinical contexts1,2. Notably, evidence also pointed to sex-specific consequences: while elevated somatic symptom burden has been associated with increased mortality risk, this association appears to be confined to men, underscoring the complex and differential health implications of somatization across sexes1. Against this backdrop, findings from the SARS-CoV-2 pandemic suggested that somatic symptoms may be particularly sensitive to large-scale psychosocial stressors. Multiple studies observed a high prevalence of somatization during the pandemic, especially among individuals infected with SARS-CoV-25,6 Beyond infection status, COVID-19-related anxiety was also associated with somatic symptoms7, alongside younger age, higher fatigue, and greater psychological symptom burden8. Taken together, these findings may support the notion that pandemic-related uncertainty, stress, and mental health strain likely amplified somatic symptom burden, extending established vulnerability patterns into a novel global crisis context9. As somatic symptoms are common in the general population and have been found to be associated with various somatic and mental health burdens and illnesses as well as with numerous sociodemographic characteristics, it seems highly important to have short and validated instruments to screen somatic symptoms in population-based epidemiological surveys. The Somatic Symptom Scale (SSS-8) is a time-efficient 8-item tool for somatic symptom burden screening that assesses the most frequent somatic symptoms such as back, chest, and joint pain, headaches, stomach or bowel problems, dizziness, fatigue and difficulty falling asleep10. The scale was derived from the Patient Health Questionnaire (PHQ-15), a validated and frequently used instrument to assess somatic symptoms11,12. The SSS-8 has been found to have high internal consistency and validity in the past10,13,14. However, data on the temporal stability of the SSS-8 are limited, and its test-retest reliability, construct validity, and temporal measurement invariance have not yet been examined in a German sample during the pandemic or across extended time periods. Assessing temporal stability and measurement invariance is crucial to ensure that observed differences reflect true change rather than measurement artefacts. Therefore, this study addresses this gap in the literature and is the first to evaluate test-retest reliability and longitudinal measurement invariance of the SSS-8 in the general population. The large data set from the Gutenberg COVID-19 Study (GCS), collected at three separate time points during the pandemic, offers a unique opportunity to derive new and sound assessments of the temporal stability (testretest-reliability) and construct validity (...truncated)