Analysis of this primary outcome will be by intention-to-treat (ITT). However, a strict ITT analysis may be hard to achieve: for example, preliminary data suggest that a considerable proportion of patients drop out before the 6 month assessment (about 20 % in each group). Our primary method to address the missing data problem will be the Inverse Probability Weighting (IPW) approach. To implement IWP, we plan to use all available outcome information.