Compliance of a Cognitive Behavioral Intervention for LBP
Compliance of a Cognitive Behavioral Intervention for LBP
Of the 701 randomised participants 598 (85%) provided 12-month follow up data (advice alone n = 199/233 (85%); advice plus cognitive behavioural intervention, n = 399/468 (85%)). For the outcome measures used in the CACE analyses the number of contributing participants ranged from 498 with complete Roland Morris questionnaire scores at 12 months to 587 with complete modified Von Korff pain scores and EQ-5D scores at 12 months, with no difference in the levels of missing data between treatment groups. Due to missing data in the outcome and predictors the number of participants used in the analyses differs for each month and outcome score. The number of participants in the ITT analysis is the same is in the CACE analysis for each month and outcome score. There was one participant randomised to the advice group who received the cognitive behavioural intervention. They were analysed as intention to treat.
Levels of attendance at the cognitive behavioural assessment and group sessions are shown in Figure 1. Of the 468 participants assigned to cognitive behavioural intervention, 174 (37%) did not achieve the compliance threshold. For the non-compliant group, 50/174 (29%) people did not attend the assessment or sessions, and 59/174 (34%) attended the assessment only. The remainder of people who were non-compliant (65/174) attended the assessment and an average of 1.5 (SD 0.50) sessions. The average number of sessions attended by the compliant group was 5.1 (SD 0.91).
(Enlarge Image)
Figure 1.
Attendance at cognitive behavioural intervention sessions by compliers and non-compliers. Number of compliers (n = 294) and non-compliers (n = 174) in the CBI group (n = 468) attending each cognitive behavioural intervention session with a maximum of six sessions plus the initial individual assessment.
We obtained reasons for non-attendance from 78 (45%) of the non-compliers. The primary reasons given for not attending were feeling unwell (18/78 (10%)), changes to work (15/78 (9%)) and family issues (14/78 (8%)). The attainment of the compliance threshold was broadly similar across the different centres (22/38 (58%) to 84/127 (66%)), as were patterns of missing data. The number of patients reaching the compliance threshold varied across the 19 therapists (3/8 (38%) to 4/5 (80%)). However, there was less deviation in the complier numbers where there were more than 10 patients per therapist (8/15 (53%) to 13/18 (72%)).
Loss to follow up was significantly associated with compliance. At 12 months 113 out of 174 (65%) non-compliers provided a modified Von Korff pain score, compared with 279 out of 294 (95%) compliers (chi squared p-value < 0.001). On the Roland Morris questionnaire 72 out of 174 (41%) non-compliers provided complete data, compared to 267 out of 294 (91%) compliers (chi squared p-value < 0.001).
Table 2 shows the baseline characteristics of the compliers and non-compliers in the intervention group. Noticeably, in comparison to non-compliers, compliers were older (mean difference 4.5 years, 95% CI 1.8–7.2), had a longer duration of back pain (mean difference 2.8 years, 95% CI 0.2–5.3), had less frequent back pain (odds ratio 0.5, 95% CI 0.3–0.8) and had lower baseline modified Von Korff pain scores (mean difference 4.6 points, 95% CI 0.9–8.2). In multi-variate analysis, two baseline factors emerged as being associated with compliance. These were age (odds ratio 1.02, 95% CI 1.01–1.04), and a worse modified Von Korff pain score (odds ratio 0.99, 95% CI 0.98–1.00).
Adjusted estimates of the mean scores on the Roland Morris questionnaire, modified Von Korff score and EQ-5D are reported by intervention arm and by compliance status in Table 3. The effect of compliance was most evident on the pain and disability outcomes at the time points closest to the intervention delivery, where compliers experienced at least a doubling of response in comparison to non-compliers. By the 12 month follow up, non-compliers had recovered to a similar level as the compliers, the only exceptions being the Modified Von Korff Disability score at 12 months, where compliers continued to report greater benefits from the cognitive behavioural intervention. Compliers experienced greater gains in EQ-5D scores at 3 months and these remained stable thereafter, whereas non-compliers reported a gradual improvement in EQ-5D, with no statistically significant difference by compliance status at either 6 or 12 months.
The ITT and CACE estimates of the treatment effect are reported in Table 4. Co-variate adjustment for the CACE model provided a statistically significant better fit for all models (Likelihood Test p < 0.001 for all models), and hence only these models are reported. In all CACE models, with the exception of the Roland Morris questionnaire, the estimate of the mean treatment difference was greater than from the ITT analysis. In nearly all comparisons, the lower bound of the 95% confidence interval was also greater.
The CACE estimate of the treatment difference between advice alone and advice plus cognitive behavioural therapy on the Roland Morris questionnaire score is 1.6 points (95% CI 0.51–2.74) at 12 months. The estimated treatment difference for compliers is 12.1 points (6.07–18.17) on the Von Korff disability score and 10.4 points (4.64–16.10) on the Von Korff pain score at 12 months. The estimated treatment difference at 12 months for compliers on the EQ-5D is 0.07 (0.01–0.14) points. At 12 months the standardised effect size is increased for all measures using the CACE analysis. Comparing the ITT estimate to the CACE estimate in Table 4, the estimate of the standardised effect size is increased from 0.31 to 0.43 on the Roland Morris questionnaire, from 0.42 to 0.60 on the Von Korff disability score and from 0.37 to 0.60 on the Von Korff pain score. There is a threefold increase in the estimate of the standardised effect size on the EQ-5D, from an ITT estimate of 0.13 to a CACE estimate of 0.36.
Estimates from CACE analyses redefining compliance as attendance at the individual assessment only, attendance at the individual assessment and one or more group therapy sessions and two or more group therapy sessions are reported in Table 5. Based on definitions of compliance with a minimum requirement as attendance at the individual assessment the estimate of the mean treatment difference is greater than from the ITT analysis for all outcomes at 6 and 12 months.
CACE model estimates and ITT estimates based on imputed datasets show a small reduction in the magnitude of the treatment difference at 3, 6 and 12 months with the exception of the Roland Morris questionnaire at 3 months. The CACE estimates remain greater than the ITT estimates and conclusion of significance of the treatment effect remains the same for all analyses based on the imputed data.
Results
Participants
Of the 701 randomised participants 598 (85%) provided 12-month follow up data (advice alone n = 199/233 (85%); advice plus cognitive behavioural intervention, n = 399/468 (85%)). For the outcome measures used in the CACE analyses the number of contributing participants ranged from 498 with complete Roland Morris questionnaire scores at 12 months to 587 with complete modified Von Korff pain scores and EQ-5D scores at 12 months, with no difference in the levels of missing data between treatment groups. Due to missing data in the outcome and predictors the number of participants used in the analyses differs for each month and outcome score. The number of participants in the ITT analysis is the same is in the CACE analysis for each month and outcome score. There was one participant randomised to the advice group who received the cognitive behavioural intervention. They were analysed as intention to treat.
Levels of attendance at the cognitive behavioural assessment and group sessions are shown in Figure 1. Of the 468 participants assigned to cognitive behavioural intervention, 174 (37%) did not achieve the compliance threshold. For the non-compliant group, 50/174 (29%) people did not attend the assessment or sessions, and 59/174 (34%) attended the assessment only. The remainder of people who were non-compliant (65/174) attended the assessment and an average of 1.5 (SD 0.50) sessions. The average number of sessions attended by the compliant group was 5.1 (SD 0.91).
(Enlarge Image)
Figure 1.
Attendance at cognitive behavioural intervention sessions by compliers and non-compliers. Number of compliers (n = 294) and non-compliers (n = 174) in the CBI group (n = 468) attending each cognitive behavioural intervention session with a maximum of six sessions plus the initial individual assessment.
We obtained reasons for non-attendance from 78 (45%) of the non-compliers. The primary reasons given for not attending were feeling unwell (18/78 (10%)), changes to work (15/78 (9%)) and family issues (14/78 (8%)). The attainment of the compliance threshold was broadly similar across the different centres (22/38 (58%) to 84/127 (66%)), as were patterns of missing data. The number of patients reaching the compliance threshold varied across the 19 therapists (3/8 (38%) to 4/5 (80%)). However, there was less deviation in the complier numbers where there were more than 10 patients per therapist (8/15 (53%) to 13/18 (72%)).
Loss to follow up was significantly associated with compliance. At 12 months 113 out of 174 (65%) non-compliers provided a modified Von Korff pain score, compared with 279 out of 294 (95%) compliers (chi squared p-value < 0.001). On the Roland Morris questionnaire 72 out of 174 (41%) non-compliers provided complete data, compared to 267 out of 294 (91%) compliers (chi squared p-value < 0.001).
Complier Characteristics
Table 2 shows the baseline characteristics of the compliers and non-compliers in the intervention group. Noticeably, in comparison to non-compliers, compliers were older (mean difference 4.5 years, 95% CI 1.8–7.2), had a longer duration of back pain (mean difference 2.8 years, 95% CI 0.2–5.3), had less frequent back pain (odds ratio 0.5, 95% CI 0.3–0.8) and had lower baseline modified Von Korff pain scores (mean difference 4.6 points, 95% CI 0.9–8.2). In multi-variate analysis, two baseline factors emerged as being associated with compliance. These were age (odds ratio 1.02, 95% CI 1.01–1.04), and a worse modified Von Korff pain score (odds ratio 0.99, 95% CI 0.98–1.00).
Adjusted estimates of the mean scores on the Roland Morris questionnaire, modified Von Korff score and EQ-5D are reported by intervention arm and by compliance status in Table 3. The effect of compliance was most evident on the pain and disability outcomes at the time points closest to the intervention delivery, where compliers experienced at least a doubling of response in comparison to non-compliers. By the 12 month follow up, non-compliers had recovered to a similar level as the compliers, the only exceptions being the Modified Von Korff Disability score at 12 months, where compliers continued to report greater benefits from the cognitive behavioural intervention. Compliers experienced greater gains in EQ-5D scores at 3 months and these remained stable thereafter, whereas non-compliers reported a gradual improvement in EQ-5D, with no statistically significant difference by compliance status at either 6 or 12 months.
Estimates of the CACE Model
The ITT and CACE estimates of the treatment effect are reported in Table 4. Co-variate adjustment for the CACE model provided a statistically significant better fit for all models (Likelihood Test p < 0.001 for all models), and hence only these models are reported. In all CACE models, with the exception of the Roland Morris questionnaire, the estimate of the mean treatment difference was greater than from the ITT analysis. In nearly all comparisons, the lower bound of the 95% confidence interval was also greater.
The CACE estimate of the treatment difference between advice alone and advice plus cognitive behavioural therapy on the Roland Morris questionnaire score is 1.6 points (95% CI 0.51–2.74) at 12 months. The estimated treatment difference for compliers is 12.1 points (6.07–18.17) on the Von Korff disability score and 10.4 points (4.64–16.10) on the Von Korff pain score at 12 months. The estimated treatment difference at 12 months for compliers on the EQ-5D is 0.07 (0.01–0.14) points. At 12 months the standardised effect size is increased for all measures using the CACE analysis. Comparing the ITT estimate to the CACE estimate in Table 4, the estimate of the standardised effect size is increased from 0.31 to 0.43 on the Roland Morris questionnaire, from 0.42 to 0.60 on the Von Korff disability score and from 0.37 to 0.60 on the Von Korff pain score. There is a threefold increase in the estimate of the standardised effect size on the EQ-5D, from an ITT estimate of 0.13 to a CACE estimate of 0.36.
Estimates from CACE analyses redefining compliance as attendance at the individual assessment only, attendance at the individual assessment and one or more group therapy sessions and two or more group therapy sessions are reported in Table 5. Based on definitions of compliance with a minimum requirement as attendance at the individual assessment the estimate of the mean treatment difference is greater than from the ITT analysis for all outcomes at 6 and 12 months.
CACE model estimates and ITT estimates based on imputed datasets show a small reduction in the magnitude of the treatment difference at 3, 6 and 12 months with the exception of the Roland Morris questionnaire at 3 months. The CACE estimates remain greater than the ITT estimates and conclusion of significance of the treatment effect remains the same for all analyses based on the imputed data.