A QQ plot designed with statistics students in mind
Usage
qq(x,ax=NA,leg=NA,cex.leg=0.8)
Arguments
x
A vector of data
ax
The name you want to call x for the x-axis (if omitted, defaults to what was passed as the first argument). Useful if the variable is a column in a dataframe.
leg
Optional argument that places a legend in the top left of the plot with the text given by leg
cex.leg
Optional argument that gives the magnification of the text in the legend
Details
This function gives a "QQ plot" that is more easily interpreted than the standard QQ plot. Instead of plotting quantiles, it plots the observed values of x versus the values expected had x come from a Normal distribution.
The distribution can be considered approximately Normal if the points stay within the upper/lower dashed red lines (with the possible exception at the far left/right) and if there is no overall global curvature.
#Distribution does not resemble a Normal data(TIPS)
qq(TIPS$Bill,ax="Bill")
#Distribution resembles aNormal data(ATTRACTF)
qq(ATTRACTF$Score,ax="Attractiveness Score")