Table 2 Descriptive statistics of baseline measures
|  | Mean ± SD | Observed range | Theoretical range | Cronbach’s alpha | Floor | Ceiling |
|---|---|---|---|---|---|---|
ODI score | 19.1 ± 15.6 | (0.0, 66.0) | (0.0, 100.0) | 0.895 | 1.4% (3) | 0.0% (0) |
HADS score | ||||||
 Depression | 5.0 ± 3.7 | (0.0, 19.0) | (0.0, 21.0) | 0.835 | 5.8% (12) | 0.0% (0) |
 Anxiety | 5.8 ± 3.7 | (0.0, 16.0) | (0.0, 21.0) | 0.860 | 4.8% (10) | 0.0% (0) |
 Total | 10.8 ± 6.9 | (0.0, 35.0) | (0.0, 42.0) | 0.908 | 3.9% (8) | 0.0% (0) |
EQ-5D VAS score | 62.9 ± 18.9 | (10.0, 97.0) | (0.0, 100.0) | NA | 0.0% (0) | 0.0% (0) |
EQ-5D-5 L score | 0.789 ± 0.191 | (− 0.044, 1.000) | (− 0.391, 1.000) | 0.843 | 0.0% (0) | 3.2% (7) |
BASFI | 2.2 ± 2.2 | (0.0, 8.9) | (0.0, 10.0) | 0.940 | 6.4% (14) | 0.0% (0) |
BASMI | 4.0 ± 1.6 | (0.7, 8.2) | (0.0, 10.0) | 0.806 | 0.0% (0) | 0.0% (0) |
SF-36 | ||||||
 Physical functioning | 74.2 ± 20.4 | (5.0, 100.0) | (0.0, 100.0) | 0.900 | 0.0% (0) | 7.4% (12) |
 Role physical | 70.7 ± 23.4 | (0.0, 100.0) | (0.0, 100.0) | 0.941 | 0.0% (0) | 13.5% (22) |
 Role emotional | 72.5 ± 25.3 | (0.0, 100.0) | (0.0, 100.0) | 0.936 | 0.0% (0) | 16.0% (26) |
 Vitality | 52.7 ± 19.7 | (0.0, 93.8) | (0.0, 100.0) | 0.792 | 0.6% (1) | 0.0% (0) |
 Emotional well-being | 67.0 ± 17.6 | (20.0, 100.0) | (0.0, 100.0) | 0.819 | 0.0% (0) | 1.9% (3) |
 Social functioning | 77.4 ± 22.0 | (12.5, 100.0) | (0.0, 100.0) | 0.846 | 0.0% (0) | 17.3% (28) |
 Bodily pain | 61.9 ± 22.3 | (10.0, 100.0) | (0.0, 100.0) | 0.852 | 0.0% (0) | 1.9% (3) |
 General health | 42.0 ± 20.1 | (0.0, 95.0) | (0.0, 100.0) | 0.823 | 1.3% (2) | 0.0% (0) |
 PCS | 44.2 ± 8.2 | (19.5, 60.7) | (0.0, 100.0) | 0.959 | 0.0% (0) | 0.0% (0) |
 MCS | 45.5 ± 10.6 | (17.3, 71.1) | (0.0, 100.0) | 0.959 | 0.0% (0) | 0.0% (0) |
BASDAI | 3.5 ± 2.0 | (0.0, 9.2) | (0.0, 10.0) | 0.905 | 0.0% (0) | 0.0% (0) |
ASDAS-CRP | 1.6 ± 1.0 | (0.0, 5.2) | NA | NA | 0.0% (0) | 0.0% (0) |