a Onset type defined as sudden (self-reported as developing fatigue in = 1 week) or gradual (developing fatigue over a period = 1 month). One subject described onset as between 1 week and one month and was not classified for this stratification. b Further stratification and analysis using the Kruskal-Wallis nonparametric test did not show different results. c Analysis performed on BMI <25 (normal) compared with >30(obese). Subjects considered overweight were not included in this particular analysis. Further stratification and analysis using the Kruskal-Wallis test showed no significant differences between the groups (results not shown.). d Illness group defined by factor analysis of symptoms followed by cluster analysis .