plot.qqline {sma} | R Documentation

## Add Line Going Through the Quantiles of a Q-Q Plot

### Description

This function adds a line to a quantile-quantile plot which passes through user defined quantiles. This function is similar to, but more general than, `qqline` because the reference distribution need not be the standard normal distribution and the quantiles need not be the first and third quartiles.
Graphical parameters may be given as arguments to `plot.qqline`.

### Usage

    plot.qqline(x, y, a=0.25, ...)

### Arguments

`x` | the reference (first) sample for the Q-Q plot, for a normal Q-Q plot this would be the quantiles of a N(0,1) random sample.
`y` | the data.
`a` | a number between 0 and 1. A line is drawn which connects the `a` and `1-a` quantile points. The default line passes through the first and third quantiles.
`...` | graphical parameters may also be supplied as arguments to the function (see `par`).

### See Also

`qqplot`, `qqnorm`, `qqline`.

### Examples

    data(MouseArray)
    # mouse.setup <- init.grid()
    # mouse.data <- init.data() ## see \emph{init.data}
    # mouse.lratio <- stat.ma(mouse.data, mouse.setup)

    ## Calculation of t-statistics
    ## cl <- c(rep(1,3), rep(2,3))
    ## mouse.t2 <- stat.t2(mouse.lratio, cl)

    ## Diagnostic plots
    plot.qq(mouse.t2$t, "Mouse")

    ## Using the QQline function
    q <- quantile(rnorm(1000))
    plot.qqline(q, mouse.t2$t)

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