# shadenormal.fnc: Shade rejection region for normal probability density... In languageR: Analyzing Linguistic Data: A Practical Introduction to Statistics

## Description

This function plots the standord normal probability density function and shades the rejection region.

## Arguments

 qnts A numeric vector with the Z-scores of the boundaries of the lower and upper rejection regions.

## Value

A plot on the graphics device.

Type shadenormal.fnc to see the code. The polygon() function used for the shaded areas takes a sequence of X and Y coordinates, connects the corresponding points, and fills the area(s) enclosed with a specified color. To understand the use of polygon(), one can best think of making a polygon with a set of pins, a thread, and a board. Outline the polygon by placing the pins on the board at the corners of the polygon. First fasten the thread to one of the pins, then connect the thread to the second pin, from there to the third pin, and so on, until the first pin has been reached. What polygon() requires as input is a vector of the X-coordinates of the pins, and a vector of their Y-coordinates. These coordinates should be in exactly the order in which the thread is to be connected from pin to pin.

For shading the left rejection area, we specify the vectors of X and Y coordinates, beginning at the leftmost point of the tail, proceding to the right edge of the shaded area, then up, and finally to the left and down to the starting point, thereby closing the polygon. The X-coordinates are therefore specified from left to right, and then from right to left. The corresponding Y-coordinates are all the zeros necessary to get from \$-3\$ to \$1.96\$ (the default, qnorm(0.025)), and then the Y-coordinates of the density in reverse order to return to where we began.

R. H. Baayen

## Examples

 1 2 3 4 ## Not run: shadenormal.fnc() ## End(Not run)

languageR documentation built on May 2, 2019, 10:02 a.m.