qqnorm {stats} | R Documentation |

## Quantile-Quantile Plots

### 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 normal quantile-quantile plot which
passes through 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, ...)
## Default S3 method:
qqnorm(y, ylim, main = "Normal Q-Q Plot",
xlab = "Theoretical Quantiles", ylab = "Sample Quantiles",
plot.it = TRUE, datax = FALSE, ...)
qqline(y, datax = FALSE, ...)
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? |

`ylim, ...` |
graphical parameters. |

### Value

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

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")

[Package

*stats* version 2.5.0

Index]