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Table 2 Baseline characteristics of randomised participants by compliance status; complier, non-complier or control

From: Treatment compliance and effectiveness of a cognitive behavioural intervention for low back pain: a complier average causal effect approach to the BeST data set

  Advice plus cognitive behavioural intervention (n = 468)
  Control Complier Non-complier Mean difference* p value
  (n = 233) (n = 294) (n = 174) (95% CI)  
Age (years) 54.1 (14.9) 55.0 (14.3) 50.5 (14.8) 4.5 (1.8, 7.2) 0.001
Sex     - 0.694
 Female 142 (60.9%) 173 (58.8%) 105 (60.3%)   
 Male 90 (38.6%) 121 (41.2%) 68 (39.1%)
 Missing 1 (0.4%) 0 1 (0.6%)
Ethnic origin - 0.258
 White 206 (88.4%) 268 (91.2%) 144 (82.8%)   
 Mixed 3 (1.3%) 2 (0.7%) 2 (1.1%)
 Asian 8 (3.4%) 9 (3.1%) 12 (6.9%)
 Black 4 (1.7%) 4 (1.4%) 3 (1.7%)
 Chinese 1 (0.4%) 1 (0.3%) 0
 Missing 11 (4.7%) 10 (3.4%) 13 (7.5%)
Severity of back pain     - 0.802
 Moderately troublesome 130 (55.8%) 157 (53.4%) 95 (54.6%)   
 Very or extremely troublesome 103 (44.2%) 137 (46.6%) 79 (45.4%)  
Age left full-time education (years) - 0.584
 ≤16 121 (51.9%) 168 (57.1%) 98 (56.3%)   
 17-19 61 (26.2%) 65 (22.1%) 39 (22.4%)  
 ≥20 49 (17.2%) 48 (16.3%) 25 (14.4%)  
 Still in full-time education 2 (0.9%) 0 1 (0.6%)  
 Missing 9 (3.9%) 13 (4.4%) 11 (6.3%)  
In employment† - 0.612
 Yes 110 (47.2%) 147 (50.0%) 91 (52.3%)   
 No 122 (52.4%) 146 (49.7%) 82 (47.1%)   
 Retired 77 (63.1%) 94 (64.4%) 36 (43.9%)   
 At home not looking for work 4 (3.3%) 12 (8.2%) 13 (15.9%)  
 Unable to work because of back pain 11 (9.0%) 12 (8.2%) 10 (12.2%)  
 Unable to work because of other illness 9 (7.4%) 10 (6.8%) 6 (7.3%)  
 Unemployed and looking for work 8 (6.6%) 1 (0.7%) 3 (3.7%)  
 In full-time education 2 (1.6%) 0 0  
 Other 3 (2.5%) 1 (0.7%) 5 (6.1%)  
 Reason not given 8 (6.6%) 16 (11.0%) 9 (11.0%)  
Duration of back pain (years since first onset) 13.2 (12.7) 14.1 (14.2) 11.4 (11.2) 2.8 (0.2, 5.3) 0.034
Frequency of back pain (past 6 weeks) - 0.009
 Everyday 162 (69.5%) 189 (64.3%) 126 (72.4%)   
 Less often than everyday 47 (20.2%) 82 (27.9%) 29 (16.7%)
 Missing 24 (10.3%) 23 (7.8%) 19 (10.9%)
Roland Morris questionnaire 8.5 (4.7) 8.6 (4.9) 9.1 (5.2) -0.4 (-1.4, 0.5) 0.357
Modified Von Korff disability 46.2 (23.8) 47.0 (23.6) 51.0 (24.1) -4.0 (-8.6, 0.5) 0.083
Modified Von Korff pain 59.4 (19.5) 57.6 (19.3) 62.2 (18.9) -4.6 (-8.2, -1.0) 0.014
EQ-5D 0.6 (0.3) 0.6 (0.3) 0.5 (0.3) 0.1 (-0.01, 0.1) 0.082
  1. Data are mean (SD) or n (%). Participants in the control group were assigned to receive advice only.
  2. *Mean difference between compliers and non-compliers in cognitive behavioural intervention arm.
  3. †Reported p values are from t test where mean differences are reported and chi-squared tests elsewhere.