In statistics, a probability plot is a graphical technique for comparing two data sets, either two sets of empirical observations, one empirical set against a theoretical set, or (more rarely) two theoretical sets against each other. It commonly means one of: In statistics, a probability plot is a graphical technique for comparing two data sets, either two sets of empirical observations, one empirical set against a theoretical set, or (more rarely) two theoretical sets against each other. It commonly means one of: The term 'probability plot' may be used to refer to both of these types of plot, or the term 'probability plot' may be used to refer specifically to a P-P plot.