check_form function

Check model formula

This function checks the input form.

check_form(form, re = NULL, ordered = FALSE)

Arguments

• form: A formula object that is used to specify the model equation. The structure is 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.

• re: A character (vector) of covariates of form with random effects. If re = NULL (the default), there are no random effects. To have random effects for the ASCs, include "ASC" in re.

• ordered: A boolean, FALSE per default. If TRUE, the choice set alternatives is assumed to be ordered from worst to best.

Returns

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.

See Also

overview_effects() for an overview of the model effects