Create random effects and fixed effects specifications from an mgcv smooth term for use in splinemixmeta.

This function is for internal use by splinemixmeta().

Usage

make_smm_smooth(
  smooth,
  data,
  vnames = character(),
  manual_fixed = FALSE,
  envir = parent.frame()
)

Arguments

smooth

A term created by mgcv::s()

data

Data frame containing the variables used in the smooth. See envir.

vnames

"a vector of names to avoid as dummy variable names in the random effects form", per mgcv::smooth2random(), to which vnames is passed.

manual_fixed

If FALSE, the unpenalized dimensions (typically a linear term) of the smooth are used as fixed effects. If TRUE, the user should provide any desired fixed effects directly. In either case, unpenalized dimensions of the smooth term are not included in the spline. See details.

envir

The environment in which to evaluate variable names if data is not provided.

Value

A list with elements basisFxns (the basis functions for the random effects) and x_fixed (the fixed effects design matrix, or NULL if manual_fixed is TRUE).

Details

This function uses mgcv::smoothCon() and mgcv::smooth2random() to obtain basis functions, penalty matrix, and (optionally) fixed effects terms from the smooth specification.

The fixed effects (if manual_fixed is FALSE) represent unpenalized directions of the smooth. Typically, this means the fixed effects will include linear terms, because splines usually penalize curvature, so any parameters that give a line are unpenalized. If one is not particularly interested in the linear terms (more generally, unpenalized terms), then the default of manual_fixed = FALSE is a good option. However, if one is interested in coefficients for the linear terms, it is important to note that when they are extracted from the basis function setup, they may be (typically will be) also re-scaled, and it is not particularly easy to determine the scaling factor. Hence, one may prefer to set manual_fixed=FALSE and provide the linear term directly in the formula argument to splinemixmeta().