A randomised controlled trial evaluated the effectiveness of an integrated care programme in facilitating the return to work for patients with chronic low back pain. The programme was a combined patient and workplace directed intervention. Control treatment was the usual care programme. Trial participants were recruited from primary and secondary care if they were aged 18-65 years, had had low back pain for more than 12 weeks, were in paid work, and had been absent or partially absent from work. In total, 66 participants were assigned to integrated care and 68 to usual care.
The primary outcome was length of time off work after randomisation until a fully sustained return to work. The study period was 12 months. Analysis was undertaken according to the principle of intention to treat and compared with those of a per protocol analysis. The results of the two analyses were similar. The duration of time off work until a fully sustained return to work was significantly shorter for patients receiving integrated care compared with usual care.
Which one of the following statements best describes the principle of per protocol analysis?
a) Patients were included in the analysis only if they agreed to follow the treatment protocol of the care programme they were allocated
b) Patients were included in the analysis only if they started the care programme they were allocated
c) Two groups of patients were compared on the basis of the treatment originally allocated
d) Two groups of patients were compared on the basis of those who completed the treatment protocol for the care programme originally allocated
Answer d is the best description.