BACKGROUND: Rigorous testing of the original Fatigue Severity Scale (FSS-9) with modern psychometric methods is warranted. OBJECTIVE: To determine the psychometric properties of the FSS-9 in multiple sclerosis (MS): internal scale validity; person response validity; unidimensionality; uniform differential item functioning; temporal stability of response patterns; and ability to separate people into distinct groups of fatigue. METHODS: Rasch analyses were conducted on data from a Norwegian and a Swedish MS cohort followed for two years. RESULTS: Item estimations in the FSS-9 did not differ between sex or levels of education but between the cohorts with regard to disability, disease course and time for evaluation, however, items 1 and 2 demonstrated unacceptable high outfit mean-square values in both cohorts. In an FSS-7 item version, items 3 and 4 in the Norwegian and 4 in the Swedish cohort demonstrated unacceptable goodness of fit but high separation indexes. In the FSS-7, the first unidimensional factor explained 87.5% (Norwegian cohort) and 86.4% (Swedish cohort) of the total variation. CONCLUSIONS: In MS, the FSS-7 demonstrates better psychometric properties than the FSS-9; items 1 and 2 neither empirically nor conceptually fit with the other seven items.
BACKGROUND: Rigorous testing of the original Fatigue Severity Scale (FSS-9) with modern psychometric methods is warranted. OBJECTIVE: To determine the psychometric properties of the FSS-9 in multiple sclerosis (MS): internal scale validity; person response validity; unidimensionality; uniform differential item functioning; temporal stability of response patterns; and ability to separate people into distinct groups of fatigue. METHODS: Rasch analyses were conducted on data from a Norwegian and a Swedish MS cohort followed for two years. RESULTS: Item estimations in the FSS-9 did not differ between sex or levels of education but between the cohorts with regard to disability, disease course and time for evaluation, however, items 1 and 2 demonstrated unacceptable high outfit mean-square values in both cohorts. In an FSS-7 item version, items 3 and 4 in the Norwegian and 4 in the Swedish cohort demonstrated unacceptable goodness of fit but high separation indexes. In the FSS-7, the first unidimensional factor explained 87.5% (Norwegian cohort) and 86.4% (Swedish cohort) of the total variation. CONCLUSIONS: In MS, the FSS-7 demonstrates better psychometric properties than the FSS-9; items 1 and 2 neither empirically nor conceptually fit with the other seven items.
Authors: Anners Lerdal; Anders Kottorp; Caryl Gay; Bradley E Aouizerat; Carmen J Portillo; Kathryn A Lee Journal: Qual Life Res Date: 2011-03-10 Impact factor: 4.147
Authors: Erik Boberg; Nadir Kadri; Jeanette Winterling; Lindsay C Davies; Andreas Björklund; Mussie Msghina; Ellen Iacobaeus; Katarina Le Blanc Journal: Haematologica Date: 2019-10-24 Impact factor: 9.941
Authors: Roy G Elbers; Marc B Rietberg; Erwin E H van Wegen; John Verhoef; Sharon F Kramer; Caroline B Terwee; Gert Kwakkel Journal: Qual Life Res Date: 2011-10-20 Impact factor: 4.147
Authors: Franco M Impellizzeri; Fiorenza Agosti; Alessandra De Col; Alessandro Sartorio Journal: Health Qual Life Outcomes Date: 2013-03-06 Impact factor: 3.186