Figure 1

Study population as classified into fatigued and non-fatigued groups. *all CFS-like respondents who did not report an exclusionary condition were invited to participate in a clinical evaluation; †3 participants had inconclusive psychiatric assessments and could not be classified; Fatigue = severe fatigue of ≥ 1 month. Exclusion = subject reported a medical or psychiatric condition that would exclude a diagnosis of CFS. Prolonged Fatigue = severe fatigue ≥ 1 month but < 6 months. Chronic fatigue = severe fatigue ≥ 6 months, but without sufficient symptoms or fatigue severity to meet the 1994 CFS research case definition1. CFS-like = appears to meet the CFS case definition [1].Insufficient Fatigue = no longer reported sufficient symptoms or fatigue severity when evaluated clinically. Explained Syndromic Fatigue = appears to meet the CFS case definition, except that an exclusionary condition was either reported or discovered upon clinical evaluation.