BackgroundThe Somatic Symptom Scale-8 (SSS-8) is a brief self-report instrument assessing somatic symptom burden derived from the PHQ-15. The aims of the present study were providing updated population norms for Germany based on a new representative sample and enabling a direct comparison with the original 2012 normative sample. In addition, the study aimed to examine the psychometric properties of the SSS-8, evaluate construct validity, and test factorial validity and measurement invariance.MethodsA representative German community sample was surveyed in 2021 (N = 2,515; 51.6% female; age range: 16–101 years). Construct validity was evaluated through latent correlations with measures of depression (PHQ-2), anxiety (GAD-2), well-being (WHO-5), and loneliness (UCLA-3). Health care utilization was predicted using negative binomial regression. Factorial validity was examined using confirmatory factor analysis with WLSMV estimation (unidimensional model and second-order factor model). Measurement invariance was tested across gender, age, gender × age, depression (PHQ-2 ≥ 3), and anxiety (GAD-2 ≥ 3). Population norms were established using SCAM-smoothed cumulative percentiles.ResultsInternal consistency was high (ω = .922, 95% CI [.915,.929]). The higher-order model (CFI = .979, TLI = .966, SRMR = .046; RMSEA = .091, 90% CI [.083,.099]) showed better fit than the unidimensional model (CFI = .961, TLI = .945, SRMR = .054; RMSEA = .115, 90% CI [.108,.123]). Strict invariance was supported for depression and anxiety. For gender, age, and gender × age, partial scalar invariance was established after freeing one item intercept (headaches). Latent correlations supported convergent and discriminant validity with depression (r = .81), anxiety (r = .76), well-being (r = -.67), and loneliness (r = .57). Each one-point increase in SSS-8 scores was associated with a 9.7% increase in doctor visits (IRR = 1.097, 95% CI [1.082, 1.112]). A cross-cohort comparison with the original normative sample (2012; N = 2,484) revealed a significant increase in somatic symptom burden (d = -0.40, 95% CI [-0.45, -0.34]).ConclusionsThe SSS-8 demonstrates good psychometric properties in a representative German community sample. Updated population norms are provided for clinical use. The observed increase in somatic symptom burden underscores the necessity of updating population norms at regular intervals.
Psychometric evaluation and community norms of the Somatic Symptom Scale-8 based on a representative German sample
Hanna Kampling

