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]