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)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.
Distinct times denoting the stopping time of time intervals.
Additional arguments to pass to the environment used to evaluate
expr.
An object of class tparams_def.
An object of class expanded_hesim_data (as
in eval_model()) expanded by the distinct times in times.
Random samples of the parameters returned by eval_rng().
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.
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().