Gems: An R package for simulating from disease progression models

Mathematical models of disease progression predict disease outcomes and are useful epidemiological tools for planners and evaluators of health interventions. the r package gems is a tool that simulates disease progression in patients and predicts the e_ect of di_erent interventions on patient outcome. disease progression is represented by a series of events (e.g.,diagnosis,treatment and death),displayed in a directed acyclic graph. the vertices correspond to disease states and the directed edges represent events. the package gems allows simulations based on a generalized multistate model that can be described by a directed acyclic graph with continuous transition-speci_c hazard functions. the user can specify an arbitrary hazard function and its parameters. the model includes parameter uncertainty,does not need to be a markov model,and may take the history of previous events into account. applications are not limited to the medical _eld and extend to other areas where multistate simulation is of interest. we provide a technical explanation of the multistate models used by gems,explain the functions of gems and their arguments,and show a sample application. © 2015,american statistical association. all rights reserved.