The log rank test

The previous two statistical questions described survival (time to event) data.1 2 The example used was a randomised controlled trial that evaluated the effectiveness of an integrated care programme compared with usual care in facilitating the return to work of patients with chronic low back pain.3 The integrated care programme was a combined patient and workplace directed intervention.

Trial participants were adults aged between 18 and 65 years who had experienced low back pain for more than 12 weeks, were in paid work, and were absent or partially absent from work. The primary outcome was duration of time off work—that is, from randomisation until a fully sustained return to work.

Participants were followed for 12 months. The survival (time to event) data for the two treatment groups were compared statistically using the log …