Table 3.

Distribution of EQ-5D and SF-6D indices.

	No. of items	Theoretical range	Observed range	Floor effect,⁎ n (%)	Ceiling effect,† n (%)	Mean (SD)	Median (IQR)	ICC of indices
Whole sample, n = 4541
EQ-5D, n = 4349	5	−0.594 to 1	−0.371 to 1.00	119 (2.7)	1850 (42.5)	0.79 (0.27)	0.85 (0.73 to 1.00)	0.61
SF-6D, n = 4176	6	0.29 to 1	0.345 to 1.00	9 (0.2)	174 (4.2)	0.77 (0.15)	0.80 (0.66 to 0.92)
Chronic pain without NC, n = 1611
EQ-5D, n = 1551	5	−0.594 to 1	−0.235 to 1.00	54 (3.8)	239 (15.4)	0.70 (0.25)	0.76 (0.69 to 0.80)	0.57
SF-6D, n = 1499	6	0.29 to 1	0.345 to 1.00	1 (0.1)	18 (1.2)	0.73 (0.14)	0.72 (0.62 to 0.86)
Chronic pain with NC, n = 399
EQ-5D, n = 373	5	−0.594 to 1	−0.371 to 1.00	64 (17.2)	14 (3.8)	0.47 (0.36)	0.62 (0.89 to 0.73)	0.44
SF-6D, n = 358	6	0.29 to 1	0.345 to 1.00	5 (1.4)	3 (0.8)	0.62 (0.15)	0.60 (0.52 to 0.71)

IQR = interquartile range; ICC = intraclass correlation coefficient, NC = neuropathic characteristics.

^⁎Floor effect, less than 0 (worse than death) for EQ-5D and minimum value for SF-6D = 0.345.

^†Ceiling effect = 1 for both instruments.