This dialog is activated by selecting the **Q-Q Plot...** command from the Plot -> Statistical Graphs menu. It can be used in order to create and customize a Q-Q (quantile-quantile) plot of the selected data column in the active table window.

The *N* valid input data values *x _{i}* are first sorted ascendingly:

- Blom
(default): s = (i - 0.375)/(N + 0.25)

- Benard
s = (i - 0.3)/(N + 0.4)

- Hazen
s = (i - 0.5)/N

- VanDerWaerden
s = i/(N + 1)

- KaplanMeier
s = i/N

The sorted values are represented on the Q-Q plot by points whose X coordinates are the *x _{i}* values and whose Y coordinates are calculated using the inverse of the cumulative distribution functions of the

There are five distributions available for Q-Q plots and the inverse of their cumulative distribution functions are calculated using the following formulas (available with muParser as script engine):

- Normal
(default): normalinv(s, m, sd), where

*m*is the arithmetic mean and*sd*is the standard deviation of the input data set.- Lognormal
logninv(s, scale, shape)

- Exponential
expinv(s, m), where

*m*is the arithmetic mean of the input data set.- Weibull
wblinv(s, scale, shape)

- Gamma
gaminv(s, shape, scale)

The *scale* and *shape* parameters that are used for
the Lognormal, Weibull and
Gamma
distributions are calculated using the maximum likelihood estimation (MLE) method.