Summary of main findings
In the original trial we had sufficient power to detect a clinically significant minimum difference in the proportion of individuals who improved their symptoms of 10% to be detected at the 1% significance level with 99% power. At 6 month follow-up we detected a difference in improvement of 11% which met the criteria for clinical significance. By long term follow up we detected a 5% difference which whilst a statistically significant improvement did not reach our threshold for clinical significance. So, at 6 years, whilst the probability of SC being superior is less than 1%, so too is the probability of the difference being greater than 10% (compared with 67% at 6 months (Figure ).
Differences in percentage improvement at 6 months and 6 years in the CNP and standard care arms (separate file).
The improvements in the CNP group shown immediately post treatment (at 3 and 6 months) had decreased (by half) at long term follow up. The follow-up took place at 6 years therefore the annual 'drop off' of effect between the groups was approximately 1% each year.
Comparison with existing literature
Although this trial has shown no clinically significant difference between treatment groups at 6 years, the statistically significant difference of 5% is an improvement on previous comparable trials which have shown no difference at all at 6 years. Maintenance of effect is rarely seen in long term follow-up studies of conservative interventions for incontinence [16
]. Glazener et al 2005 [17
] in their 6 year follow-up of a randomised controlled trial of conservative management of postnatal urinary and faecal incontinence found no differences between their intervention and standard care groups at 6 years following a 1 year difference of 9%. Similarly Agur et al (2008) [18
] in their eight year follow-up of an RCT of antenatal pelvic floor muscle training found no difference between the groups at follow-up.
Strengths and limitations of the study
This study gained a response rate of 87%, this was a high response rate compared to similar follow-ups at six years [17
Secondary outcomes of improvement in impact, perception of their problem and satisfaction with quality of life seen at 3 and 6 months were not maintained at long term follow-up.
For costs at follow-up our most notable finding was that NHS costs in the CNP arm were higher than those in the SC arm, though not significantly so. This finding was surprising given the lack of differences found in the other variables examined in the course of this study. However, this may be due to the fact that those in the CNP arm were familiar with seeking and obtaining specialist help with their urinary symptoms. A higher propensity to seek primary care contacts may in turn lead to more referrals to secondary care and more inpatient care and surgeries. There were no differences in individuals own borne costs suggesting that measures taken by individuals to manage their own symptoms were similar in the two groups. We found that NHS costs were similar for men and women. We were able to exclude many prostate related costs from our calculations as we could identify prostate related inpatient stays and drug usage from our estimates (including these would increase NHS costs from £92 to £123). Some of the costs related to male urinary symptoms would still be related to prostate conditions however as the reasons for services such as contact with GP may not be related to the underlying condition.
Since the 2002 publication of the ICS standardisation document [14
] the symptom subgroups of USI, OAB and mixed have become more established and we wanted to explore whether long term outcomes varied according to these subgroups. If certain subgroups of individuals did better at long term follow-up than others, future services could specifically identify and target these groups for services in the future. We only found that those individuals initially classified with 'mixed' incontinence did statistically better in the CNP arm. This may be due to the nature of the service which was better able to provide more complex care tackling more than one problem and following up outcomes to amend treatment interventions in a way that standard care is less able to do. In addition mixed symptoms tend to be more severe and may have responded well to the comprehensive CNP service.
At long term follow-up there is the potential risk of contamination between treatment arms once a trial is finished. This was not the case in this study as the CNP service was specifically set up for study purposes and funding of the service was not possible following completion of the research programme. The availability of generic continence services post trial for each group was identical. Whilst these services would draw on the education and experience of nurses trained within the trial programme, there was no possibility that those from standard care would have access to the successful service and could be contaminated.
Although the study was not explicitly designed as a cluster randomised trial, 220 (8%) patients were in the same household, i.e. 110 household pairs. The reduction in power due to this cluster was minimal - the study was designed to have over 95% power in order to adequately power a number of small embedded trials. In order to assess any impact on the results, a logistic regression model for the primary outcome (improvement compared to baseline) and which allowed for the effect of clustering was used. This gave identical results to those presented.
We were also interested to know whether there were any specific predictors of improvement, that again would enable service providers to target services of the future to specific groups, however there were no clear predictors of improvement.