`hesim`

is a modular and computationally efficient R package for health economic simulation modeling and decision analysis that provides a general framework for integrating statistical analyses with economic evaluation. The package supports cohort discrete time state transition models (DTSTMs), N-state partitioned survival models (PSMs), and individual-level continuous time state transition models (CTSTMs), encompassing both Markov (time-homogeneous and time-inhomogeneous) and semi-Markov processes. It heavily utilizes `Rcpp`

and `data.table`

, making individual-patient simulation, probabilistic sensitivity analysis (PSA), and incorporation of patient heterogeneity fast.

Features of the current version can be summarized as follows:

- Cohort DTSTMs, N-state PSMs, and individual-level CTSTMs that encompass Markov and semi-Markov processes
- Options to build models via mathematical expressions using nonstandard evaluation or directly from fitted statistical models
- Parameter estimates from either an R based model or from an external source
- Convenience functions for sampling model parameters from parametric distributions or via bootstrapping
- Parameter uncertainty propagated with PSA
- Modeling patient heterogeneity
- Performing cost-effectiveness analyses and representing decision uncertainty from PSAs
- Simulation code written in
`C++`

to boost performance