This function checks the input form.
check_form(form, re = NULL, ordered = FALSE)A list that contains the following elements:
The input form.
The name choice of the dependent variable in form.
The input re.
A list vars of three character vectors of covariate names of
the three covariate types.
A boolean ASC, determining whether the model has ASCs.
[formula]
A model description with the structure choice ~ A | B | C, where
choice is the name of the dependent variable (the choices),
A are names of alternative and choice situation specific
covariates with a coefficient that is constant across alternatives,
B are names of choice situation specific covariates with
alternative specific coefficients,
and C are names of alternative and choice situation specific
covariates with alternative specific coefficients.
Multiple covariates (of one type) are separated by a + sign.
By default, alternative specific constants (ASCs) are added to the model.
They can be removed by adding +0 in the second spot.
In the ordered probit model (ordered = TRUE), the formula
object has the simple structure choice ~ A. ASCs are not estimated.
[character() | NULL]
Names of covariates with random effects.
If re = NULL (the default), there are no random effects.
To have random effects for the ASCs, include "ASC" in re.
[logical(1)]
If TRUE, the choice set alternatives is assumed to be ordered
from worst to best.
overview_effects() for an overview of the model effects