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Quantile-quantile plot

`qqplot(`

displays a quantile-quantile plot of the
quantiles of the sample data `x`

)`x`

versus the theoretical
quantile values from a normal distribution. If the distribution of
`x`

is normal, then the data plot appears linear.

`qqplot`

plots each data point in
`x`

using plus sign (`'+'`

) markers and
draws two reference lines that represent the theoretical distribution. A solid
reference line connects the first and third quartiles of the data, and a dashed
reference line extends the solid line to the ends of the data.

`qqplot(___,`

displays
a quantile-quantile plot with the quantiles specified in the vector `pvec`

)`pvec`

,
using any of the previous syntaxes.

returns
the handles (`h`

= qqplot(___)`h`

) to the lines in the quantile-quantile
plot.