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Fatigue Severity Scale (FSS)
Freely available for non-profit research:
For pharmaceutical studies: Fatigue Severity Scale copyright belongs to Dr. Lauren Krupp. Permission required for use.
Supplemental - Highly Recommended: Myalgic encephalomyelitis/Chronic fatigue syndrome (ME/CFS) as a subjective self-reported measure of fatigue
Supplemental: Parkinson's Disease (PD) Multiple Sclerosis (MS), Spinal Cord Injury (SCI), and SCI-Pediatric for adolescents at least 16 years of age
Exploratory: Amyotrophic Lateral Sclerosis (ALS)
Short Description of Instrument
Construct measured: Impact of fatigue on patient's daily life
Generic vs. disease specific: Generic
Means of administration: Interview or paper and pencil
Intended respondent: Patient
# of items: 9
# of subscales and names of sub-scales: N/A
# of items per sub-scale: N/A
Comments/Special Instructions
Scoring: Each item is a statement on fatigue that the subject rates from 1 (strongly disagree) to 7 (strongly agree). The scoring is done by calculating the average response to the questions (adding up all the answers and dividing by nine). Absolute thresholds for clinical meaningfulness have not been formally defined, although scores greater than 4 to 5 are considered indicative of significant fatigue.
Background: The FSS was developed and initial validation completed in patients with multiple sclerosis and systemic lupus, but the scale has been used in studies of fatigue in multiple other diseases including SCI. The FSS was recently suggested for both a screening and a rating instrument by a MDS Task Force. There are several more expansive scales that may be appropriate in a given study.
Strengths/Weaknesses: Administration only takes a few minutes. Limited data on psychometric properties of the FSS in North American MS populations are available.
Advantages: The FSS is brief to administer. It measures not just fatigue but the effect of fatigue on function. This measure has been widely used in ME/CFS.
Limitations: The FSS may be susceptible to ceiling effects as many ME/CFS patients scored close to or at the maximum score.
Psychometric Properties: NOTE: Summary of demonstrated properties below includes data from both N. American and European MS studies.
Reliability: Cronbach's alpha .81 to .89; Cronbach's alpha in a Swiss MS cohort = .94. Convergent Validity: correlates with MFIS Spearman r=.68, p<.0001 in a majority RRMS Spanish population; r=.66, p<.0001 in a four-country European study; Kendall's Tau-b = 0.645, Dutch FSS; high correlation with fatigue VAS in a Swiss MS cohort (r=.79). Divergent Validity: Modest correlation with Beck Depression Inventory (r = .48) and EDSS (r= .45, p<.0001; r= 0.33, p<.0001 after adjusting for BDI) in an RRMS predominate Spanish population; correlation with EDSS (r = .34, p<.01) in a Swiss MS cohort. Sensitivity: Dutch FSS not responsive to change (z = -1.417, p= .156) following a four-week rehabilitation program.
Original validation: It is correlated with single item, vitality visual analogue scale. The FSS measure differentiates fatigue in MS, lupus, ME/CFS and other fatiguing illnesses from healthy controls. It differentiates fatigue in ME/CFS which is higher than in MS and also fatigue in ME/CFS vs. depression. This measure is sensitive to treatment change in ME/CFS. The fatigue link to function is important, also known as fatigability, as similar fatigue levels across patients may be associated with widely divergent levels of impairment. Sensitivity, specificity, positive predictive value, etc. results would require an analysis of FSS scores from with CFS-diagnosed patients, subsyndromal patients and healthy controls which has not been done. Also there is not a gold standard for ME/CFS diagnosis to make such comparisons.
Administration: The FSS only takes a few minutes to administer.
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ME/CFS-Specific References:
Jason LA, Evans M, Brown M, Porter N, Brown A, Hunnell J, Anderson V, Lerch A. Fatigue Scales and Chronic Fatigue Syndrome: Issues of Sensitivity and Specificity.Disabil Stud Q. 2011;31(1):1375.


Document last updated June 2020