• Christopher R Knox, Ranjit Lall, Zara Hansen, and Sarah E Lamb.
• Warwick Clinical Trials Unit, Warwick Medical School, University of Warwick, Coventry CV7 1AL, UK. sarah.lamb@ndorms.ox.ac.uk.
• Bmc Musculoskel Dis. 2014 Jan 14; 15: 17.

BackgroundGroup cognitive behavioural intervention (CBI) is effective in reducing low-back pain and disability in comparison to advice in primary care. The aim of this analysis was to investigate the impact of compliance on estimates of treatment effect and to identify factors associated with compliance.MethodsIn this multicentre trial, 701 adults with troublesome sub-acute or chronic low-back pain were recruited from 56 general practices. Participants were randomised to advice (control n = 233) or advice plus CBI (n = 468). Compliance was specified a priori as attending a minimum of three group sessions and the individual assessment. We estimated the complier average causal effect (CACE) of treatment.ResultsComparison of the CACE estimate of the mean treatment difference to the intention-to-treat (ITT) estimate at 12 months showed a greater benefit of CBI amongst participants compliant with treatment on the Roland Morris Questionnaire (CACE: 1.6 points, 95% CI 0.51 to 2.74; ITT: 1.3 points, 95% CI 0.55 to 2.07), the Modified Von Korff disability score (CACE: 12.1 points, 95% CI 6.07 to 18.17; ITT: 8.6 points, 95% CI 4.58 to 12.64) and the Modified von Korff pain score (CACE: 10.4 points, 95% CI 4.64 to 16.10; ITT: 7.0 points, 95% CI 3.26 to 10.74). People who were non-compliant were younger and had higher pain scores at randomisation.ConclusionsTreatment compliance is important in the effectiveness of group CBI. Younger people and those with more pain are at greater risk of non-compliance.Trial RegistrationCurrent Controlled Trials ISRCTN54717854.

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