2.2. Measures
2.2.1. Overview
Mediating variables are those responsible for all or part of the effects of a treatment on outcome. Therefore, a mediator variable must change during treatment, be associated with treatment, and have an effect on outcome. In this trial, most of our mediator variables were specified in our heuristic model and developed prior to the funding of the study. Sleep disturbance was added because it is known to have an important effect on back pain. Hours of back exercise were added as a proxy for physical movement.