A 7-item version of the fatigue severity scale has better psychometric properties among HIV-infected adults: an application of a Rasch model
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- Lerdal, A., Kottorp, A., Gay, C. et al. Qual Life Res (2011) 20: 1447. doi:10.1007/s11136-011-9877-8
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To examine the psychometric properties of the 9-item Fatigue Severity Scale (FSS) using a Rasch model application.
A convenience sample of HIV-infected adults was recruited, and a subset of the sample was assessed at 6-month intervals for 2 years. Socio-demographic, clinical, and symptom data were collected by self-report questionnaires. CD4 T-cell count and viral load measures were obtained from medical records. The Rasch analysis included 316 participants with 698 valid questionnaires.
FSS item 2 did not advanced monotonically, and items 1 and 2 did not show acceptable goodness-of-fit to the Rasch model. A reduced FSS 7-item version demonstrated acceptable goodness-of-fit and explained 61.2% of the total variance in the scale. In the FSS-7 item version, no uniform Differential Item Functioning was found in relation to time of evaluation or to any of the socio-demographic or clinical variables.
This study demonstrated that the FSS-7 has better psychometric properties than the FSS-9 in this HIV sample and that responses to the different items are comparable over time and unrelated to socio-demographic and clinical variables.
KeywordsFatigueHIVPsychometricsSymptomsQuality of life
Acquired immune deficiency syndrome
Body mass index
Differential item functioning
Daytime sleepiness subscale
Fatigue severity scale
General sleep disturbance scale
Human immunodeficiency virus
Principal component analysis