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. `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`.

### 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 2.1.0 Index]