The overall log-likelihood is then given by the sum of LL it terms over i (the two wards) and is maximized using unconstrained optimization with the Nelder-Mead algorithm [49] as implemented in the function optim in R version 2.11.1 (www.project-r.org). Approximate 95% confidence intervals (CIs) were derived by inverting the square matrix of second-order partial derivatives of the loglikelihood function, i.e. the Hessian.