R: Define and evaluate transformed parameter expressions

define_tparams {hesim}

R Documentation

Define and evaluate transformed parameter expressions

Description

Transformed parameter expressions are used to transform the parameter values sampled with eval_rng() as a function of input data (treatment strategies and patients) and time intervals. These functions are used when evaluating an object of class model_def defined using define_model(). The transformed parameters are ultimately converted into tparams objects and used to simulate outcomes with an economic model.

Usage

define_tparams(expr, times = NULL, ...)

eval_tparams(x, input_data, rng_params)

Arguments

`expr`	Expressions used to transform parameters. As with `define_rng()`, braces should be used so that the result of the last expression within the braces is evaluated. The expression must return a named list with the following possible elements: tpmatrix: The transition probability matrix used to simulate transition probabilities in the economic model. This should either be the output of `tpmatrix()` or a 3-dimensional array as in `tparams_transprobs()`. utility: The utility values to attach to states and used to simulate quality-adjusted life-years in the economic model. Either a vector (in which case utility is the same in each health state) or a `data.table`/`data.frame`/`matrix` with a column for each (non-death) health state. costs: A named list of costs for each category used to simulate costs in the economic model. Each element of the list must be in the same format as `utility`.
`times`	Distinct times denoting the stopping time of time intervals.
`...`	Additional arguments to pass to the environment used to evaluate `expr`.
`x`	An object of class `tparams_def`.
`input_data`	An object of class expanded_hesim_data (as in `eval_model()`) expanded by the distinct times in `times`.
`rng_params`	Random samples of the parameters returned by `eval_rng()`.

Details

define_tparams() is evaluated when creating economic models as a function of model_def objects defined with define_model(). Operations are "vectorized" in the sense that they are performed for each unique combination of input_data and params. expr is evaluated in an environment including each variable from input_data, all elements of rng_params, and a variable time containing the values from times. The time variable can be used to create models where parameters vary as a function of time. eval_tparams() is not exported and is only meant for use within eval_model().

Value