sirt (version 1.5-0)

rasch.prox: PROX Estimation Method for the Rasch Model

Description

This function estimates the Rasch model using the PROX algorithm (cited in Wright & Stone, 1999).

Usage

rasch.prox(dat, dat.resp = 1 - is.na(dat), freq=rep(1,nrow(dat)) , 
    conv = 0.001, maxiter = 30, progress = FALSE)

Arguments

dat

An $N \times I$ data frame of dichotomous response data. NAs are not allowed and must be indicated by zero entries in the response indicator matrix dat.resp.

dat.resp

An $N \times I$ indicator data frame of nonmissing item responses.

freq

A vector of frequencies (or weights) of all rows in data frame dat.

conv

Convergence criterion for item parameters

maxiter

Maximum number of iterations

progress

Display progress?

Value

• A list with following entries
• b
  Estimated item difficulties
• theta
  Estimated person abilities
• iter
  Number of iterations
• sigma.i
  Item standard deviations
• sigma.n
  Person standard deviations

References

Wright, B., & Stone, W. (1999). Measurement Essentials. Wilmington: Wide Range.

Examples

#############################################################################
# EXAMPLE 1: PROX data.read
#############################################################################

data(data.read)
mod <- rasch.prox( data.read )
mod$b       # item difficulties