Psychometric validation of the Portuguese version of the LKCS as a brief screening tool for chronic stress across the lifespan

Chronic stress is a major public health concern associated with adverse psychological, behavioral, and health outcomes across the lifespan. Reliable and brief screening instruments are essential for the early identification of individuals at risk and for the evaluation of stress-management interventions. The Leipziger Kurzfragebogen für Chronischen Stress (LKCS) is a short self-report instrument designed to assess key indicators of chronic stress. Although preliminary Portuguese studies have shown promising results, evidence based on large and heterogeneous samples remains limited. The present study aimed to examine the psychometric properties of the Portuguese version of the LKCS in a large community sample. A cross-sectional web-based survey was conducted with an initial sample of 1,942 Portuguese participants aged 15–67 years. Participants were recruited using non-probability convenience sampling through educational and occupational settings, including schools, universities, and professional institutions. Six participants with incomplete responses to one or more LKCS items were excluded through complete-case analysis, resulting in a final analytical sample of 1,936 participants. Psychometric evaluation included descriptive and reliability analyses, principal axis factoring based on polychoric correlations, ordinal confirmatory factor analysis using diagonally weighted least squares estimation, and multigroup measurement-invariance testing across gender. Known-groups analyses examined differences according to gender, age group, and socio-professional context. The LKCS demonstrated good internal consistency (Cronbach’s α = 0.83; CR = 0.87). Principal axis factoring supported a one-factor solution accounting for 47.92% of the common variance, with loadings ranging from 0.572 to 0.793. Ordinal confirmatory factor analysis yielded significant standardized loadings from 0.568 to 0.797 and mixed global fit (scaled CFI = 0.961; TLI = 0.941; RMSEA = 0.114; SRMR = 0.039). AVE was 0.49, close to the conventional 0.50 criterion. Configural, threshold, and threshold-plus-loading invariance across gender were supported. Age-group differences were not significant; small differences were observed by gender and socio-professional context. The Portuguese version of the LKCS demonstrated satisfactory reliability and a coherent one-factor structure, with qualified support from ordinal confirmatory factor analysis and evidence of threshold and factor-loading invariance across gender. Although AVE was slightly below the conventional criterion, the findings support the use of the LKCS as a brief dimensional measure of chronic stress for research and population-screening purposes, rather than as a stand-alone diagnostic instrument.