draw.tetra {psych} R Documentation

## Draw a correlation ellipse and two normal curves to demonstrate tetrachoric correlation

### Description

A graphic of a correlation ellipse divided into 4 regions based upon x and y cutpoints on two normal distributions. This is also an example of using the layout function. Draw a bivariate density plot to show how tetrachorics work.

### Usage

draw.tetra(r, t1, t2,shade=TRUE)
draw.cor(r=.5,expand=10,theta=30,phi=30,N=101,nbcol=30,box=TRUE,
main="Bivariate density  rho = ",cuts=NULL,all=TRUE,ellipses=TRUE,ze=.15)


### Arguments

 r the underlying Pearson correlation defines the shape of the ellipse t1 X is cut at tau t2 Y is cut at Tau shade shade the diagram (default is TRUE) expand The relative height of the z axis theta The angle to rotate the x-y plane phi The angle above the plane to view the graph N The grid resolution nbcol The color resolution box Draw the axes main The main title cuts Should the graphic show cuts (e.g., cuts=c(0,0)) all Show all four parts of the tetrachoric ellipses Draw a correlation ellipse ze height of the ellipse if requested

### Details

A graphic demonstration of the tetrachoric correlation. Used for teaching purposes. The default values are for a correlation of .5 with cuts at 1 and 1. Any other values are possible. The code is also a demonstration of how to use the layout function for complex graphics using base graphics.

### Author(s)

William Revelle

tetrachoric to find tetrachoric correlations, irt.fa and fa.poly to use them in factor analyses, scatter.hist to show correlations and histograms.

### Examples

#if(require(mvtnorm)) {
#draw.tetra(.5,1,1)
#draw.tetra(.8,2,1)} else {print("draw.tetra requires the mvtnorm package")
#draw.cor(.5,cuts=c(0,0))}

draw.tetra(.5,1,1)
draw.tetra(.8,2,1)
draw.cor(.5,cuts=c(0,0))


[Package psych version 2.3.6 ]