Table 1.

Definitions of ME/CFS symptom severity classes by Weighted Standing Time (WST), with reference to standing time and difficulty. (a) Four categories featuring a healthy control category, and a severity scale from mild to severe symptoms. (b) Three severity classes where the healthy control cohort (0) was combined with the mild category (1) from Table (a) to increase sample size for random forest algorithm interrogation (WST). All ME/CFS cases fulfilled the ICC diagnostic criteria.

(a)
Category	n	WST	Definition of ME/CFS Symptom Severity Class (Post ICC)
0	17	14.29–18.57	Healthy—No disease; All stood 20 min at Difficulty 1–4
1	19	15.71–18.57	Mild severity; All stood 20 min at Difficulty 1–3
2	38	6.43–14.29	Moderate Severity; All stood 20 min at Difficulty 4–10
3	23	0.0–2.57	Severe; All <20 min standing + Difficulty 12 or 14
(b)
Category	n	WST	Definition of ME/CFS Symptom Severity Class (Post ICC)
0 *	36	14.29–18.57	Healthy + Mild symptoms; All stood 20 min at Difficulty 1–4
1	38	6.43–14.29	Moderate Severity; All stood 20 min at Difficulty 4–10
2	23	0.0–2.57	Severe; All <20 min standing + Difficulty 12 or 14

ICC—International Consensus Criteria (Diagnostic criteria for ME/CFS [12]). Standing time scale—0 to 20 min, with measurements at every two minutes; Standing difficulty scale—0 represents no difficulty, 14 represents extreme difficulty resulting in the inability to stand upright for a minimum of 10 min. * (0 + 1 from Table 1a).