R: Probability Plot

probplot {e1071} | R Documentation

## Probability Plot

### Description

Generates a probability plot for a specified theoretical distribution, i.e., basically a `qqplot` where the y-axis is labeled with probabilities instead of quantiles. The function is mainly intended for teaching the concept of quantile plots.

### Usage

    probplot(x, qdist=qnorm, probs=NULL, line=TRUE,
             xlab=NULL, ylab="Probability in %", ...)
    ## S3 method for class 'probplot'
    lines(x, h=NULL, v=NULL, bend=FALSE, ...)

### Arguments

`x` | A data vector for `probplot`, an object of class `probplot` for the `lines` method.
`qdist` | A character string or a function for the quantiles of the target distribution.
`probs` | Vector of probabilities at which horizontal lines should be drawn.
`line` | Add a line passing through the quartiles to the plot?
`xlab, ylab` | Graphical parameters.
`h` | The y-value for a horizontal line.
`v` | The x-value for a vertical line.
`bend` | If `TRUE`, lines are “bent” at the quartile line, else regular `abline`s are added. See examples.
`...` | Further arguments for `qdist` and graphical parameters for lines.

### Author(s)

Friedrich Leisch

### See Also

`qqplot`

### Examples

    ## a simple example
    x <- rnorm(100, mean=5)
    probplot(x)

    ## the same with horizontal tickmarks at the y-axis
    opar <- par("las")
    par(las=1)
    probplot(x)

    ## this should show the lack of fit at the tails
    probplot(x, "qunif")

    ## for increasing degrees of freedom the t-distribution converges to
    ## normal
    probplot(x, qt, df=1)
    probplot(x, qt, df=3)
    probplot(x, qt, df=10)
    probplot(x, qt, df=100)

    ## manually add the line through the quartiles
    p <- probplot(x, line=FALSE)
    lines(p, col="green", lty=2, lwd=2)

    ## Make the line at prob=0.5 red
    lines(p, h=0.5, col="red")

    ### The following use the estimted distribution given by the green
    ### line:

    ## What is the probability that x is smaller than 7?
    lines(p, v=7, bend=TRUE, col="blue")

    ## Median and 90% confidence interval
    lines(p, h=.5, col="red", lwd=3, bend=TRUE)
    lines(p, h=c(.05, .95), col="red", lwd=2, lty=3, bend=TRUE)

    par(opar)

[Package e1071 version 1.7-4 Index]