Complete data on the SBT and ÖMPSQ was available for 130/244 (53%) patients. The sample was 60% female, with a mean (±SD) age of 44 (±10.0) and disability score (RMDQ) of 8.6 (±6.6). Back pain episode durations were varied with 25% < 1 month, 27% 1–6 months, and 48% >6 months, and 43% reported being ‘very’ or ‘extremely’ bothered by their back pain. The median scores (range) for SBT and ÖMPSQ were 4.5 (0–9) and 98.8 (26.3–189.0), respectively.
The Spearman’s rank correlation coefficients for the SBT total scores and psychosocial subscale scores with the ÖMPSQ scores were 0.802 and 0.769 respectively. The magnitude of the reported correlation coefficients was therefore, ‘large’ and was similar to the correlation between disability (RMDQ) and the subgroup tools (SBT = 0.813; ÖMPSQ = 0.830). Figures for fear (TSK) (SBT psychological subscale = 0.659; ÖMPSQ = 0.683) and catastrophising (PCS) (SBT = 0.671; ÖMPSQ = 0.656) were lower but also classified as ‘large’. presents box plot graphs of the ÖMPSQ total score against the SBT (a) total score and (b) psychosocial subscale and demonstrate that increasing ÖMPSQ scores, correlated with higher SBT scores across the full range of both instrument scales.
Box plot graph of the ÖMPSQ total scores against (a) the SBT total score and (b) the SBT psychosocial subscale.
The proportions of patients allocated to ‘low’, ‘medium’ and ‘high’ risk groups by the SBT and ÖMPSQ were 40% cf 40%, 35% cf 22%, and 25% cf 38%, respectively. The ‘low’ risk proportion was therefore the same, but the SBT allocated considerably fewer patients to the ‘high’ risk group, but significantly more patients to the ‘medium’ risk group than the ÖMPSQ (McNemar Bowker test p = 0.022).
Observed agreement between the two instruments for allocation to ‘low’, ‘medium’ and ‘high’ risk groups, is presented in , with absolute agreement in 62% of patients. Weighted Cohen’s kappa for agreement in allocation to the three subgroups beyond chance was ‘moderate’, 0.57 (95% CI 0.47–0.68, p = 0.000). Agreement about allocation to the ‘low’ risk group alone (‘low’ versus ‘medium’ or ‘high’) was ‘substantial’ at 0.63 (95% CIs 0.50–0.77, p = 0.000).
Observed agreement of SBT and ÖMPSQ subgroups (n = 130).
The clinical characteristics of the subgroups (‘low’, ‘medium’ and ‘high’) derived using the SBT and ÖMPSQ are presented in . The characteristics of the ‘low’ risk groups were almost identical (e.g. both had an RMDQ median of 2 and a pain NRS of 1.7). The ‘medium’ risk groups differed only slightly with higher pain and disability scores among those allocated by the SBT and the ‘high’ risk groups were also very similar although the ÖMPSQ ‘high’ risk group had slightly more females and had longer episode durations. However, these differences between the clinical characteristics in the ‘medium’ and ‘high’ risk groups produced by both tools were not statistically significant (p > 0.05).
Medians [inter-quartile ranges] of clinical characteristics by low, medium and high subgroups derived using SBT and ÖMPSQ cut-offs.
The ability of the two instruments’ total scores (and SBT subscale scores) to discriminate patients defined as ‘cases’ on reference standards is given in and . There were no significant differences in the discriminative abilities of the SBT and ÖMPSQ scales for ‘cases’ of disability, catastrophising, fear, comorbid pain, time off work or episode duration reference standards. The SBT was significantly better for discriminating bothersome and referred leg pain ‘cases’ while the ÖMPSQ scores was better at discriminating ‘cases’ of pain intensity.
Fig. 2 Receiver operating characteristic (ROC) curves of ÖMPSQ and SBT scores against reference standards for (a) disability and pain, (b) catastrophising and fear, (c) referred leg pain and bothersomeness, and (d) time off work and episode duration. (more ...)