Rankit

sample of six items is taken from a normally distributed population with expected value 0 and variance 1 (the standard normal distribution) and then sorted into increasing order, the expected values of the resulting order statistics are: Suppose the numbers in a data set are Then one may sort these and line them up with the corresponding rankits; in order they are which yields the points: These points are then plotted as the vertical and horizontal coordinates of a scatter plot.

Alternatively, rather than sort the data points, one may rank them, and rearrange the rankits accordingly.

In large samples from a normally distributed population, such a plot will approximate a straight line.

Substantial deviations from straightness are considered evidence against normality of the distribution.

Rankit plots are usually used to visually demonstrate whether data are from a specified probability distribution.