An interesting aspect of running a clinical trial is that researchers nominate a primary outcome before starting the study. Because many outcomes will be measured, an occasional outcome measure may show a statistically significant result by chance alone. Therefore the researchers single out their primary outcome so that - if a significant result is obtained on that one particular outcome - it can be concluded that it is truly due to the treatment because it unlikely to be due to chance alone.

A group of researchers in Brazil followed this convention in their recent trial of neurodynamic therapy for chronic nerve-related leg pain - that is, the type of pain that often occurs in conjuction with back pain. Neurodynamic therapy involves passive or active movements, which aimed to desensitise the overly sensitised nervous system by restoring its ability to tolerate external forces such as movement and compression. Participants in the study received 4 treatments over 2 weeks, with each session lasting up to 25 minutes. The study did not find any significant effects on the primary outcomes: leg pain and disability at 2 weeks. Interestingly, however, many of the secondary outcome measures did show significant benefits!