# qqnorm {stats}

### Description

`qqnorm`

is a generic function the default method of which produces a normal QQ plot of the values in `y`

. `qqline`

adds a line to a “theoretical”, by default normal, quantile-quantile plot which passes through the `probs`

quantiles, by default the first and third quartiles.

`qqplot`

produces a QQ plot of two datasets.

Graphical parameters may be given as arguments to `qqnorm`

, `qqplot`

and `qqline`

.

### Usage

qqnorm(y, ...) ## S3 method for class 'default': qqnorm((y, ylim, main = "Normal Q-Q Plot", xlab = "Theoretical Quantiles", ylab = "Sample Quantiles", plot.it = TRUE, datax = FALSE, ...) qqline(y, datax = FALSE, distribution = qnorm, probs = c(0.25, 0.75), qtype = 7, ...) qqplot(x, y, plot.it = TRUE, xlab = deparse(substitute(x)), ylab = deparse(substitute(y)), ...))

### Arguments

- x
- The first sample for
`qqplot`

. - y
- The second or only data sample.
- xlab, ylab, main
- plot labels. The
`xlab`

and`ylab`

refer to the y and x axes respectively if`datax = TRUE`

. - plot.it
- logical. Should the result be plotted?
- datax
- logical. Should data values be on the x-axis?
- distribution
- quantile function for reference theoretical distribution.
- probs
- numeric vector of length two, representing probabilities. Corresponding quantile pairs define the line drawn.
- qtype
- the
`type`

of quantile computation used in`quantile`

. - ylim, ...
- graphical parameters.

### Values

For `qqnorm`

and `qqplot`

, a list with components

- x
- The x coordinates of the points that were/would be plotted
- y
- The original
`y`

vector, i.e., the corresponding y coordinates*including*.`NA`

s

### References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) *The New S Language*. Wadsworth & Brooks/Cole.

### See Also

`ppoints`

, used by `qqnorm`

to generate approximations to expected order statistics for a normal distribution.

### Examples

require(graphics) y <- rt(200, df = 5) qqnorm(y); qqline(y, col = 2) qqplot(y, rt(300, df = 5)) qqnorm(precip, ylab = "Precipitation [in/yr] for 70 US cities") ## "QQ-Chisquare" : -------------------------- y <- rchisq(500, df = 3) ## Q-Q plot for Chi^2 data against true theoretical distribution: qqplot(qchisq(ppoints(500), df = 3), y, main = expression("Q-Q plot for" ~~ {chi^2}[nu == 3])) qqline(y, distribution = function(p) qchisq(p, df = 3), prob = c(0.1, 0.6), col = 2) mtext("qqline(*, dist = qchisq(., df=3), prob = c(0.1, 0.6))")

Documentation reproduced from R 3.0.2. License: GPL-2.