collapse_W {eRm} R Documentation

## Convenient Collapsing of LLRA Design Matrix

### Description

Collapses columns of a design matrix for LLRA to specify different parameter restrictions in LLRA.

### Usage

collapse_W(W, listItems, newNames)


### Arguments

 W A design matrix (for LLRA), typically from a call to build_W or component \$W from LLRA or LPCM listItems A list of numeric vectors. Each component of the list specifies columns to be collapsed together. newNames An (optional) character vector specifying the names of the collapsed effects.

### Details

This function is a convenience function to collapse a design matrix, i.e. to specify linear trend or treatment effects and so on. Collapsing here means that effects in columns are summed up. For this, a list of numeric vectors with the column indices of columns to be collapsed have to be passed to the function. For example, if you want to collapse column 3, 6 and 8 into one new effect and 1, 4 and 9 into another it needs to be passed with list(c(3,6,8),c(1,4,9)).

The new effects can be given names by passing a character vector to the function with equal length as the list.

### Value

An LLRA design matrix as described by Hatzinger and Rusch (2009). This can be passed as the W argument to LLRA or LPCM.

Thomas Rusch

### References

Hatzinger, R. and Rusch, T. (2009) IRT models with relaxed assumptions in eRm: A manual-like instruction. Psychology Science Quarterly, 51, pp. 87–120.

The function to build design matrices from scratch, build_W.

### Examples

##An LLRA with 2 treatment groups and 1 baseline group, 5 items and 4
##time points. Item 1 is dichotomous, all others have 3, 4, 5, 6
##categories respectively.
groupvec <-rep(1:3*5,each=20)
W <- build_W(llraDat2a, nitems=5, mpoints=4, grp_n=c(10,20,40), groupvec=groupvec,itmgrps=1:5)

#There are 55 parameters to be estimated
dim(W)

#Imposing a linear trend for the second item ,i.e. parameters in
#columns 32, 37  and 42 need to be collapsed into a single column.
collItems1 <- list(c(32,37,42))
newNames1 <- c("trend.I2")
Wstar1 <- collapse_W(W,collItems1)

#53 parameters need to be estimated
dim(Wstar1)


[Package eRm version 1.0-2 Index]