Table 1 Characteristics of study population.
VariableAll ME/CFS
(n = 298)
Short-duration
ME/CFS
(≤3 years)
(n = 52)
Long-duration
ME/CFS
(>3 years)
(n = 246)
Control
(n = 348)
All ME/CFS
versus control
Short- versus
long-duration
ME/CFS
versus control
P*P
Sex, n (%)0.800.95
  Female220 (73.8)39 (75.0)181 (73.6)260 (74.7)
  Male78 (26.2)13 (25.0)65 (26.4)88 (25.3)
Age [mean (SD)]48.5 (12.4)40.5 (13.6)50.2 (11.4)48.5 (12.0)0.95<0.0001
Illness duration, years [mean (SD)]13.2 (9.2)1.7 (0.8)15.6 (8.2)
MFI mental fatigue subscale score [mean (SD)]15.3 (3.6)15.2 (3.7)15.3 (3.6)6.2 (2.7)§<0.0001<0.0001
Race, n (%)0.540.77
  White292 (98.0)52 (100.0)240 (97.6)337 (96.8)
  African American1 (0.3)0 (0.0)1 (0.4)5 (1.4)
  Asian3 (1.0)0 (0.0)3 (1.2)4 (1.1)
  Other2 (0.7)0 (0.0)2 (0.8)2 (0.6)
Site, n (%)0.800.22
  Boston, MA54 (18.1)4 (7.7)50 (20.3)55 (15.8)
  Miami, FL57 (19.1)9 (17.3)48 (19.5)67 (19.3)
  New York, NY67 (22.5)15 (28.8)52 (21.1)72 (20.7)
  Palo Alto, CA23 (7.7)1 (1.9)22 (8.9)23 (6.6)
  Salt Lake City, UT46 (15.4)11 (21.2)35 (14.2)65 (18.7)
  Sierra, NV51 (17.1)12 (23.1)39 (15.9)66 (19.0)
Months of sample acquisition, n (%)||0.02<0.0001**
  January to March77 (25.9)11 (21.2)66 (26.9)95 (27.3)
  April to June72 (24.2)17 (32.7)55 (22.4)90 (25.9)
  July to September26 (8.8)11 (21.2)15 (6.1)53 (15.2)
  October to December122 (41.1)13 (25.0)109 (44.5)110 (31.6)

*Sex, race, site, and months of sample acquisition, χ2 test; age and MFI, Kruskal-Wallis test (three-group comparisons) and Mann-Whitney U tests (two-group comparisons).

†Significant intergroup comparisons for age: short versus long duration and short duration versus control, both P < 0.0001.

n = 238 (MFI scores missing for 8 long-duration subjects).

§n = 341 (MFI scores missing for 7 control subjects).

¶Significant intergroup comparisons for MFI subscale: short duration versus control and long duration versus control, both P < 0.0001.

||Blood draw date missing for one ME/CFS case.

**Significant intergroup comparisons for months of sample acquisition: short versus long duration, P = 0.001.