Normal probability plot

`h = normplot(X)`

`h = normplot(X)`

displays
a normal probability plot of the data in `X`

. For
matrix `X`

, normplot displays a line for each column
of `X`

. `h`

is a handle to the plotted
lines.

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.

The purpose of a normal probability plot is to graphically assess
whether the data in `X`

could come from a normal
distribution. If the data are normal the plot will be linear. Other
distribution types will introduce curvature in the plot. `normplot`

uses
midpoint probability plotting positions. Use `probplot`

when
the data included censored observations.

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