sirt (version 0.31-20)

tetrachoric2: Tetrachoric Correlation Matrix

Description

This function estimates a tetrachoric correlation matrix according to the Tucker method (Method 2 of Froemel, 1971).

Usage

tetrachoric2(dat, delta = 0.007, maxit = 1000000, cor.smooth=TRUE)

Arguments

dat

A data frame of dichotomous response

delta

The step parameter. It is set by default to $2^{-7}$ which is approximately .007.

maxit

Maximum number of iterations.

cor.smooth

Should smoothing of the tetrachoric correlation matrix be performed to ensure positive definiteness. Choosing cor.smooth=TRUE, the function cor.smooth from the psych package is used.

Value

• A list with following entries
• tau
  Item thresholds
• rho
  Tetrachoric correlation matrix

References

Froemel, E. C.(1971). A comparison of computer routines for the calculation of the tetrachoric correlation coefficient. Psychometrika, 36, 165-174.

See Also

See also the tetrachoric function in the psych package.

Examples

data(data.read)	
t2 <- tetrachoric2( data.read )