The frequency of the chronic fatigue syndrome in patients with symptoms of persistent fatigue.
Manu, P, Lane, T J, Matthews, D A·Annals of internal medicine·1988
This study looked at 135 people with severe fatigue lasting at least 6 months to see how many actually had ME/CFS. The researchers found that only 6 patients (about 4%) met the criteria for ME/CFS, while most of the others had psychiatric conditions like depression or anxiety that were causing their fatigue. This suggests that ME/CFS is quite rare among people presenting with fatigue symptoms.