E2 ModerateHigher confidencePEM not requiredMethods-PaperPeer-reviewedReviewed
Standard · 3 min
The assessment of fatigue: Psychometric qualities and norms for the Checklist individual strength.
Worm-Smeitink, M, Gielissen, M, Bloot, L et al. · Journal of psychosomatic research · 2017 · DOI
Quick Summary
This study tested a questionnaire called the Checklist Individual Strength (CIS) that measures different types of fatigue, including how tired people feel, difficulty concentrating, lack of motivation, and reduced activity levels. Researchers gave this questionnaire to nearly 2,300 healthy people and over 5,000 patients with chronic fatigue to see if it accurately identifies severe fatigue. They found the CIS works well for measuring fatigue and recommended adjusting the score that indicates 'severe fatigue' from 35 to 40 points for ME/CFS research.
Why It Matters
The CIS is widely used in ME/CFS clinical practice and research to measure fatigue severity and monitor treatment response. This study provides evidence that the CIS is a reliable, valid tool for assessing fatigue and establishes appropriate cut-off scores specific to ME/CFS populations, improving diagnostic accuracy and consistency across research studies.
Observed Findings
The CIS four-factor structure (fatigue severity, concentration problems, reduced motivation, activity) was replicated in the general population sample.
Internal consistency reliability coefficients ranged from 0.84–0.95 across subscales; test–retest reliability ranged from 0.74–0.86.
Correlations between CIS subscales and other fatigue measures (Chalder Fatigue Questionnaire, SF-36 Vitality, EORTC QLQ-C30) were moderate to high.
The original cut-off score of 35 produced a 17% false positive rate in distinguishing CFS patients from healthy controls.
A revised cut-off of 40 points is recommended for CFS research to reduce false positives.
Inferred Conclusions
The CIS is a valid and reliable tool for measuring fatigue severity and related dimensions in both general and clinical populations.
A fatigue severity cut-off score of 40 points (rather than 35) is more appropriate for CFS research to minimize false positive cases.
Normative data for the general population, CFS patients, and other medical conditions enables interpretation of individual CIS scores in clinical and research contexts.
Remaining Questions
How does the CIS perform in detecting changes in fatigue over time within individual ME/CFS patients (responsiveness/sensitivity to change)?
What This Study Does Not Prove
This study validates a fatigue measurement tool but does not identify causes of ME/CFS fatigue, explain mechanisms underlying different fatigue dimensions, or determine whether fatigue severity scores predict outcomes or treatment response. The study is cross-sectional, so it cannot establish how fatigue changes over time or what factors drive disease progression.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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