E2 ModerateModerate confidencePEM not requiredCross-SectionalPeer-reviewedReviewed
Standard · 3 min
Correlations among Epworth Sleepiness Scale scores, multiple sleep latency tests and psychological symptoms.
Olson, L G, Cole, M F, Ambrogetti, A · Journal of sleep research · 1998 · DOI
Quick Summary
This study looked at whether a simple questionnaire about daytime sleepiness (the Epworth Sleepiness Scale) actually measures the same thing as a more complex sleep test that measures how quickly people fall asleep. The researchers found that these two tests don't measure the same thing—the questionnaire is influenced by mood and psychological symptoms, while the objective sleep test is not.
Why It Matters
For ME/CFS patients, this study is important because many experience both fatigue and psychological symptoms, and clinicians often rely on simple questionnaires to assess sleepiness. Understanding that self-reported sleepiness questionnaires are influenced by mood and psychological factors—not just by actual sleep physiology—helps explain why ME/CFS patients may report severe fatigue even when objective sleep measures appear relatively normal, and supports the need for multifaceted assessment approaches.
Observed Findings
ESS score and mean sleep latency showed weak but significant negative correlation (rho = -0.30, p < 0.0001).
ESS correlated with psychological symptoms (SCL-90 subscales) except psychoticism; MSLT did not show this correlation.
ESS scores correlated with total sleep time but not sleep efficiency or apnoea/hypopnoea index.
ESS ≥10 had poor sensitivity and specificity for identifying pathologically short sleep latency (<10 min or <5 min).
MSL correlated with total sleep time and sleep efficiency but not with apnoea/hypopnoea index.
Inferred Conclusions
The ESS and MSLT measure different constructs and are not interchangeable for assessing sleepiness.
Psychological factors significantly influence ESS scores but not objective MSLT measurements.
ESS alone cannot reliably identify or exclude objective sleepiness as measured by MSLT.
Subjective and objective measures of sleepiness require independent assessment rather than substitution.
Remaining Questions
Why do psychological symptoms influence subjective sleepiness ratings but not objective MSLT measurements?
What This Study Does Not Prove
This study does not prove that psychological symptoms cause poor sleep or fatigue—only that they correlate with subjective sleepiness ratings. The cross-sectional design cannot establish causality or direction of effect. The study also does not evaluate whether ME/CFS patients specifically have different patterns than other diagnostic groups, limiting generalisability of findings to this population.
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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