Produce a Line through a Normal QQ-Plot

DESCRIPTION:

This function fits and plots a line through a normal QQ-plot.

USAGE:

qqline(x, ...)
qqline(x, weights = NULL, freq = NULL, ...)

REQUIRED ARGUMENTS:

x
a numeric vector, typically a residual vector.

OPTIONAL ARGUMENTS:

weights
NULL, or vector of weights the same length as x. Quartiles are calculated for the weighted distribution with probabilities proportional to weights on the values of x.
freq
NULL, or vector the same length as x, used to replicate values of x. Quartiles are calculated for the weighted distribution with probabilities proportional to freq (or product of weights and freq) on the values of x.
...
graphics parameters may be passed to abline (which actually draws the line).

VALUE:

a vector (returned invisibly) containing the intercept and slope of the line.

SIDE EFFECTS:

plots a line through the first and third quartile of the data, and the corresponding quantiles of the standard normal distribution.

DETAILS:

This is generally used after a call to qqnorm.

SEE ALSO:

, , .

EXAMPLES:

qqnorm(car.time)
qqline(car.time, col=3)