which has been shown to be a uniform density. This explains why the q-q plot on standardized data is always close to the line y = x when the model is correct.
Finally, scientists have used special graph paper for years to make relationships linear (straight lines). The most common example used to be semi-log paper, on which points following the formula y = aebx appear linear. This follows of course since log(y) = log(a) + bx, which is the equation for a straight line. The q-q plots may be thought of as being “probability graph paper” that makes a plot of the ordered data values into a straight line. Every density has its own special probability graph paper.