normplot (Statistics Toolbox)

Normal probability plot for graphical normality testing

Syntax

```
normplot(X)
h = normplot(X)
```

Description

normplot(X) displays a normal probability plot of the data in X. For matrix X, normplot displays a line for each column of X.

The plot has the sample data displayed with the plot symbol '+'. Superimposed on the plot is a line joining the first and third quartiles of each column of X (a robust linear fit of the sample order statistics.) This line is extrapolated out to the ends of the sample to help evaluate the linearity of the data.

If the data does come from a normal distribution, the plot will appear linear. Other probability density functions will introduce curvature in the plot.

h = normplot(X) returns a handle to the plotted lines.

Examples

Generate a normal sample and a normal probability plot of the data.

x = normrnd(0,1,50,1);
h = normplot(x);

The plot is linear, indicating that you can model the sample by a normal distribution.

normpdf normrnd