define_tparams function

Define and evaluate transformed parameter expressions

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.

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().

Returns

define_tparams() returns an object of class tparams_def, which is a list containing the unevaluated "transformation" expressions passed to expr, times, and any additional arguments passed to ... . eval_tparams() evaluates the tparams_def object and should return a list of transformed parameter objects.

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().

See Also

define_model(), define_rng()