Exploring the psychometric properties of the fatigue severity scale: results from a systematic review and reliability meta-analysis

Introduction: Fatigue is a multifactorial phenomenon that affects individuals across several conditions. Fatigue Severity Scale (FSS) is a widely used questionnaire to measure perceived fatigue. This systematic review aims to identify the psychometric properties of FSS across different populations where it has been validated. Methods: The study selection process was conducted from April 2024 to January 2025. The databases used to identify included studies were MEDLINE (via PubMed), SCOPUS, Web of Science, and CINAHL (via EBSCO). The risk of bias was evaluated using the COSMIN checklist. For the meta-analysis, studies reporting the internal consistency of the scale were analyzed. Results: At the end of the selection process, 59 articles were included in the review; the sample sizes ranged from 20 to 2017 participants, and the mean age spanned from 21,86 to 68,1 years. Conclusion: The FSS is a valid and reliable instrument for fatigue assessment. It would be desirable to investigate heterogeneity; it would be beneficial to investigate responsiveness and to explore the settings in which it is used. Another advise would be to calculate cutoff in healthy subjects to better understand fatigue symptoms and the differences in perception between populations.