Preliminary verifications of the assumptions and the Bland Altman limit of the compliance graphs were carried out with Stata version 9.2 . The numerical results of the hierarchical Bayes models were derived from the computer simulation in WinBUGS  (see additional file 2). Simulations of size N = 50,000 were performed in four parallel chains (with overrelaxation) after a burn-in period of 10,000 iterations, and samples from each iteration 10 were then stored and used. The convergence of the final samples was verified using visual diagrams from simulation historians and modified Gelman Rubin statistics . 95% of credible regions (95% of CR) corresponded to the 2.5 and 97.5 percentiles of the distribution of variable interests.