mreg (version 1.2.1)

paper: An example of a function to calculate the effect on the location that depends on previous outcome in an mreg model

Description

In a regression model one may want to let the linear predictor depend on previous values of the outcome variable in longitudinal data. When the outcome variable is missing we can still do this but we have to create a function that calculates a vector of linear predictors with one element for each of the possible preceding values of the outcome.

Usage

paper(x, y, mod.Z)

Value

A numeric vector the same length as x that will be added to the linear predictor. It also has two subsidiary attributes: par.names names to be used to label the associated coefficients, and par.dim the length of this vector of coefficients.

Arguments

x

is a vector of possible values the previous value of the response could take.

y

is an vector of the coefficients. Its length is specified in the mreg function by the argument modify.p.

mod.Z

vector of observed covariates that may interact with the unobserved preceding outcome corresponding to the observation. It is taken from the model.frame produced by the mod.formula argument in mreg.

Details

This is an example function that was used in the paper referred to below. The user may write their own function as long as it takes the arguments specified above and returns a vector the same length as x that will be added to the linear predictor. It is up to the user to ensure that their function identifies the correct column of mod.Z using indices ([] that correspond to the desired variables in mod.formula. If any function other than unity (which does nothing to the linear predictor) is used then it is not possible to produce fitted values or residuals.

See Also

unity mreg

Examples

## The function is currently defined as
function(x,y, mod.Z){
  #x is the imputed response
  #y is the set of parameters
 #mod.Z is a VECTOR/matrix of explanatory variables
 rad.type <- cut(x, breaks=c(-1,0,4,9,50))
 if( is.vector(mod.Z)){
   arthdur.first <- rep(mod.Z[2],length(x))
 }
 else{
   arthdur.first <- rep(mod.Z[1,2], length(x))
 }
 X <- model.matrix( ~rad.type+I(x==0):arthdur.first)
 structure( X[,-1, drop=FALSE]%*%y, par.names= colnames( X)[-1],par.dim=dim(X)[2]-1)
}