Clark, M R, Katon, W, Russo, J et al. · The American journal of medicine · 1995 · DOI
This study followed 78 patients with chronic fatigue for about 2.5 years to understand why some people recover while others continue to struggle. Researchers found that people were more likely to have ongoing symptoms if they had multiple unexplained physical symptoms, a history of depression-like mood disorder, longer-lasting fatigue, less formal education, and were older than 38. Importantly, standard blood tests and immune system measurements did not predict who would improve.
This study identifies potentially modifiable psychological and social factors (such as mood disorders and education level) that may sustain chronic fatigue symptoms, independent of traditional medical markers. Understanding predictors of persistence helps clinicians identify high-risk patients early and may guide interventions targeting mood and symptom burden. These findings suggest that functional recovery involves more than just treating underlying viral or immunologic causes.
This study does not prove that psychological factors *cause* persistent fatigue—only that they are associated with worse outcomes. The study cannot establish whether dysthymia and multiple somatic symptoms are primary drivers of persistence or consequences of prolonged illness. The cross-sectional nature of baseline assessment means temporal relationships between predictive factors and outcomes remain unclear, and no randomized intervention trials were conducted to test causality.
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 →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Clark, M R, Katon, W, Russo, J, Kith, P, Sintay, M, & Buchwald, D (1995). Chronic fatigue: risk factors for symptom persistence in a 2 1/2-year follow-up study.. The American journal of medicine. https://doi.org/10.1016/S0002-9343(99)80403-3
BibTeX
@article{mecfsatlas-clark-1995-chronic-fatigue,
author = {Clark, M R and Katon, W and Russo, J and Kith, P and Sintay, M and Buchwald, D},
title = {Chronic fatigue: risk factors for symptom persistence in a 2 1/2-year follow-up study.},
journal = {The American journal of medicine},
year = {1995},
doi = {10.1016/S0002-9343(99)80403-3},
note = {PubMed: 7847436},
url = {https://www.mecfsatlas.com/evidence/clark-1995-chronic-fatigue},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/clark-1995-chronic-fatigue
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