as.mudfold {mudfold}

Function for calculating MUDFOLD statistics for a given unfolding scale.

Description

This function calculates the MUDFOLD statistics for data whose columns are assumed to be ranked to the order they are provided. The resulting object from the as.mudfold function is an object of S3 class "mdf", for which generic functions print, summary, and plot are available.

Usage

as.mudfold(data,estimation="rank")

Arguments

data

: A binary matrix or data.frame containing the responses of nrow(data) persons to ncol(data) items. Missing values in data are not allowed.

estimation

: This argument controls the nonparametric estimation method for person locations. By deafult this argument equals to "rank" and implies that Van Schuur's estimator will be used in order to infer the person parameters. The user can set this argument to "quantile" and then an estimator proposed by Johnson is applied.

Details

The function as.mudfold calculates MUDFOLD statistics for a given scale. Descriptive statistics, observed errors, expected errors, scalability coefficients, iso statistic values, are calculated for items and the scale. The user can obtain a summary table for the given scale with the summary function which is designed for "mdf" class objects.

Value

The function as.mudfold returns a list with the same components as the mudfold function except the information that concerns the item selection algorithm. The list contains the following:

CALL

A list where its components provide information for the function call.

CHECK

A list where its components provide information from the data checking step.

DESCRIPTIVES

A list with descriptive statistics for the data.

MUDFOLD_INFO

A list with three main components. The first component is called triple_stats and is a list where in each element contains the observed errors, expected errors, and scalability coefficients for each item triple. The second element is called first_step and informs the user that the first step of the item selection algorithm is not applied in the as.mudfold function. The third element of this list is called second_step and is also a list with the MUDFOLD statistics and parameter estimates for the given scale.

Author(s)

Spyros E. Balafas (auth.), Wim P. Krijnen (auth.), Wendy J. Post (contr.), Ernst C. Wit (auth.)

Maintainer: Spyros E. Balafas ([e-mail])

References

W.H. Van Schuur.(1984). Structure in Political Beliefs: A New Model for Stochastic Unfolding with Application to European Party Activists. CT Press.

W.J. Post. (1992). Nonparametric Unfolding Models: A Latent Structure Approach. M & T series. DSWO Press.

W.J. Post. and T.AB. Snijders. (1993).Nonparametric unfolding models for dichotomous data. Methodika.

M.S. Johnson. (2006). Nonparametric Estimation of Item and Respondent Locations from Unfolding-type Items. Psychometrica

See Also

mudfold

Examples

## Not run: 
## pick a number for setting the seed
n.seed <- 11

## Simulate an unfolding scale
simulation <- mudfoldsim(N=6, n=100, seed=n.seed)

## get the data
dat <- simulation$dat

## true order
true_order <- simulation$true_ord

## check MUDFOLD statistics for the random simulated rank order
mud_stats1 <- as.mudfold(dat)

# get the summary 
summary(mud_stats1)

## check MUDFOLD statistics for the true item rank order
mud_stats2 <- as.mudfold(dat[,true_order])

# get the summary for the true item rank order
summary(mud_stats2)

## End(Not run)