R: Q-Q Plot with Theoretical Distribution

qqmath {lattice} | R Documentation

## Q-Q Plot with Theoretical Distribution

### Description

Quantile-Quantile plot of a sample and a theoretical distribution

### Usage

    qqmath(formula, distribution = qnorm, f.value = NULL, ...)

### Arguments

`formula` | formula of the form `~ x | g1 * g2 * ...`, where `x` must be a numeric.
`distribution` | a quantile function that takes a vector of probabilities as argument and produces the corresponding quantiles. Possible values are `qnorm,qunif` etc. Distributions with other required arguments need to be passed in as user defined functions. This is also passed in as an argument to the panel function (though not used by the default panel function), and the prepanel function if specified, for use in the bery commonly used `(pre)panel.qqmathline`.
`f.value` | optional function of a single integer (representing sample size), returning a vector of probabilities corresponding to which quantiles should be plotted. The typical value for this argument is `ppoints`, which is also the S-PLUS default. If specified, the probabilities generated by this function is used for the plotted quantiles, using the `quantile` function for the sample, and the `distribution` argument for the theoretical distribution. `f.value` defaults to `NULL`, which has the effect of using `ppoints` for the quantiles of the theoretical distribution, but the exact data values for the sample. This is similar to what happens for `qqnorm`.
`...` | Other arguments

### Details

`qqmath` produces a Q-Q plot of the given sample and a theoretical distribution. The default behaviour of `qqmath` is different from the corresponding S-PLUS function, but is similar to `qqnorm`. See the entry for `f.value` for specifics.

This and all other high level Trellis functions have several arguments in common. These are extensively documented only in the help page for `xyplot`, which should be consulted to learn more detailed usage.

### Value

An object of class ``trellis''. The `update' method can be used to update components of the object and the `print' method (usually called by default) will plot it on an appropriate plotting device.

### Author(s)

Deepayan Sarkar deepayan@stat.wisc.edu

### See Also

`xyplot`, `panel.qqmath`, `panel.qqmathline`, `prepanel.qqmathline`, `Lattice`, `quantile`

### Examples

    qqmath(~ rnorm(100), distribution = function(p) qt(p, df = 10))
    data(singer)
    qqmath(~ height | voice.part, aspect = 1, data = singer,
           prepanel = prepanel.qqmathline,
           panel = function(x, y) {
              panel.qqmathline(y, distribution = qnorm)
              panel.qqmath(x, y)
           })

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