psych (version 1.0-95)

draw.tetra: 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.

Usage

draw.tetra(r, t1, t2,shade=TRUE)

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)

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.

See Also

tetrachoric, irt.fa

Examples

Run this code
if(require(mvtnorm)) {
draw.tetra(.5,1,1)
draw.tetra(.8,2,1)} else {print("draw.tetra requires the mvtnorm package")}

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