Jason, Leonard A, Brown, Abigail, Clyne, Erin et al. · Evaluation & the health professions · 2012 · DOI
This study looked at patients diagnosed with chronic fatigue syndrome (CFS) using an older definition and compared how many of them would also meet two newer, stricter definitions: ME/CFS and ME. Researchers found that patients meeting the newer, stricter definitions had more severe symptoms and greater disability than those who only met the older CFS definition. This suggests that the newer definitions may help doctors identify the most severely affected patients.
Understanding which diagnostic criteria identify the most severely affected patients is critical for both clinical care and research recruitment. These findings validate the use of stricter case definitions (ME/CFS and ME) for identifying more homogeneous, severely affected populations, which may improve treatment outcomes and research quality by reducing heterogeneity within study cohorts.
This study does not prove that the newer definitions are more 'correct' or that patients not meeting stricter criteria have less valid diagnoses. It only demonstrates that stricter definitions select for greater severity; it cannot establish whether these definitions better reflect the biological basis of the illness or predict prognosis and treatment response.
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
Jason, Leonard A, Brown, Abigail, Clyne, Erin, Bartgis, Lindsey, Evans, Meredyth, & Brown, Molly (2012). Contrasting case definitions for chronic fatigue syndrome, Myalgic Encephalomyelitis/chronic fatigue syndrome and myalgic encephalomyelitis.. Evaluation & the health professions. https://doi.org/10.1177/0163278711424281
BibTeX
@article{mecfsatlas-jason-2012-contrasting-case,
author = {Jason, Leonard A and Brown, Abigail and Clyne, Erin and Bartgis, Lindsey and Evans, Meredyth and Brown, Molly},
title = {Contrasting case definitions for chronic fatigue syndrome, Myalgic Encephalomyelitis/chronic fatigue syndrome and myalgic encephalomyelitis.},
journal = {Evaluation & the health professions},
year = {2012},
doi = {10.1177/0163278711424281},
note = {PubMed: 22158691},
url = {https://www.mecfsatlas.com/evidence/jason-2012-contrasting-case},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-29. https://www.mecfsatlas.com/evidence/jason-2012-contrasting-case
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