This function plots the standord normal probability density function and shades the rejection region.
shadenormal.fnc(qnts = c(0.025, 0.975))A numeric vector with the Z-scores of the boundaries of the lower and upper rejection regions.
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.
# NOT RUN {
shadenormal.fnc()
# }
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