jml: Joint Maximum Likelihood Estimation for Rasch Item Parameters
In wasabi1989/MiscPsycho: Miscellaneous Psychometric Analyses

Description Usage Arguments Details Value Author(s) Examples

JML is used to estimate item parameters for the Rasch model.

jml(...)
## Default S3 method:
jml(dat, con = 1e-3, bias=FALSE, ...)
## S3 method for class 'formula'
jml(formula, data, na.action, subset, con = 1e-3, bias = FALSE, ...)

`formula`	an object of class `"formula"` (or one that can be coerced to that class): a symbolic description of the model to be fitted. The details of model specification are given under `Details`.
`data`	an optional data frame, list or environment (or object coercible by `as.data.frame` to a data frame) containing the variables in the model. If not found in `data`, the variables are taken from `environment(formula)`, typically the environment from which `jml` is called.
`dat`	A data frame or matrix with item responses. Implemented only for the jml.default method.
`na.action`	a function which indicates what should happen when the data contain `NA`s. Defaults to `getOption("na.action")`.
`subset`	an optional vector specifying a subset of observations to be used.
`con`	Convergence criterion
`bias`	Implements the correction for bias as described by Wright and Stone
`...`	Not implemented

Models for jml are specified symbolically. A typical model has the form ~item1 + item2 where the terms to the right of the ~ are the columns of the data matrix containing the binary item responses.

A list with class "jml" containing the following components:

`Estimate`	the value of Rasch item parameter (b-value)
`Std.Error`	the standard error of the item parameter
`Infit`	The Rasch infit statistic
`Outfit`	The Rasch outfit statistic
`Iterations`	the number of Newton-Raphson iterations used
`model.frame`	the data matrix used for estimating item parameters. In JML estimation, individuals with all items correct and all items incorrect cannot be used in the calibration. Hence, they are dropped from the original data matrix provided by the `data` argument.

Harold Doran

set.seed(1234)
tmp <- data.frame(item1 = sample(c(0,1), 20, replace=TRUE), item2 = sample(c(0,1), 20, replace=TRUE),
item3 = sample(c(0,1), 20, replace=TRUE),item4 = sample(c(0,1), 20, replace=TRUE),item5 = sample(c(0,1), 20, replace=TRUE))

## Formula interface
fm1 <- jml(~ item1 + item2 + item3 + item4 + item5, data = tmp)
summary(fm1)
coef(fm1)
plot(fm1)

## Default interface
fm1 <- jml(tmp)
summary(fm1)