Exploring the validity of the Chalder Fatigue scale in chronic fatigue syndrome.
Morriss, R K, Wearden, A J, Mullis, R · Journal of psychosomatic research · 1998 · DOI
Quick Summary
This study tested whether the Chalder Fatigue Scale—a common questionnaire used to measure tiredness in ME/CFS patients—actually measures what it claims to measure. Researchers analyzed responses from 136 ME/CFS patients and found that fatigue has four distinct components: mental tiredness (linked to thinking problems), sleep difficulties, physical weakness (linked to low fitness), and depression. The results suggest the 11-item version of the scale works better than the original 14-item version for measuring fatigue in ME/CFS.
Why It Matters
Understanding what the Chalder Fatigue Scale actually measures is crucial for ME/CFS research, as this instrument is widely used in clinical trials and patient assessments. This study provides evidence that the scale captures distinct dimensions of fatigue—cognitive, sleep-related, and physical—allowing researchers and clinicians to better interpret results and tailor assessments to individual patient experiences.
Observed Findings
Four distinct fatigue factors were identified explaining 67% of total variance in the Chalder scale responses
Cognitive fatigue (Factor 1) correlated with subjective cognitive difficulties, concentration problems, and deficits in paired associate learning
Physical fatigue (Factor 3) showed inverse correlations with grip strength, peak VO2, peak heart rate, and functional work capacity
Sleep-related fatigue (Factor 2) correlated with sleep maintenance difficulties
Depression-related fatigue (Factor 4) correlated with both interview-based and self-rated depression measures
Inferred Conclusions
The Chalder Fatigue Scale validly captures multiple distinct dimensions of fatigue in ME/CFS patients rather than a single construct
Mental/cognitive and physical fatigue subscales should be analyzed separately for more precise assessment
The 11-item version (excluding 'loss of interest') provides a more valid measurement tool than the original 14-item version
Fatigue in ME/CFS has meaningful biological correlates including cardiovascular fitness and strength
Remaining Questions
How do these four fatigue factors change over time, and which are most responsive to treatment interventions?
What This Study Does Not Prove
This study does not establish which factors cause the others—only that they co-occur and correlate with specific symptoms. As a cross-sectional analysis, it cannot determine whether fatigue leads to depression, depression causes fatigue, or they share a common biological cause. The findings also do not address how these fatigue dimensions change over time or respond to treatment.