R: plot seats-votes curves

plot.seatsVotes {pscl} | R Documentation

## plot seats-votes curves

### Description

Plot seats-votes curves produced by `seatsVotes`

### Usage

    ## S3 method for class 'seatsVotes'
    plot(x, type = c("seatsVotes", "density"),
                    legend = "bottomright", transform=FALSE, ...)

### Arguments

`x` | an object of class `seatsVotes`
`type` | character, partially matching the options above; see details
`legend` | where to put the legend when plotting with `type="seatsVotes"`
`transform` | logical, whether to transform the vote shares for `type="density"`; see Details
`...` | arguments passed to or from other functions (e.g., options for the `density` function, when `type="density"`)

### Details

A seats-votes curve (with various annotations) is produced with option `type="seatsVotes"`.

A density plot of the vote shares is produced with `type="density"`. A bimodal density corresponds to an electoral system with a proliferation of safe seats for both parties, and a seats-votes curve that is relatively flat (or “unresponsive”) in the neighborhood of average district-level vote shares of 50 percent. The density is fitted using the defaults in the `density` function, but with the density constrained to fall to zero at the extremes of the data, via the `from` and `to` options to density. A `rug` is added to the density plot.

If `transform=TRUE`, the vote shares are transformed prior to plotting, so as to reduce the extent to which extreme vote shares close to zero or 1 determine the shape of the density (i.e., this option is available only for plots of `type="density"`). The transformation is a sinusoidal function, a scaled “log-odds/inverse-log-odds” function mapping from (0,1) to (0,1): i.e., f(x) = g(kh(x)) where h(x) is the log-odds transformation h(x) = log[x/(1-x)], k is a scaling parameter set to sqrt(3), and g(x) is the inverse-log-odds transformation g(x) = exp(x)/[1+exp(x)]. Note that this transformation is cosmetic, with the effect of assigning more of the graphing region to be devoted to marginal seats.

### Value

The function performs the requested plots and exits silently with `invisible{NULL}`.

### Author(s)

Simon Jackman simon.jackman@sydney.edu.au

### See Also

`density`, `rug`

### Examples

    data(ca2006)
    x <- ca2006$D/(ca2006$D+ca2006$R)
    sv <- seatsVotes(x,
                     desc="Democratic Vote Shares, California 2006 congressional elections")

    plot(sv)
    plot(sv,type="density")
    plot(sv,type="density",transform=TRUE)

[Package pscl version 1.5.2 Index]