R: Plot Error Bars and Confidence Intervals

plotCI {gplots} | R Documentation

## Plot Error Bars and Confidence Intervals

### Description

Given a set of x and y values and interval width or upper and lower bounds, plot the points with error bars. This can be a useful tool for visualizing confidence intervals.

### Usage

    plotCI(x, y = NULL, uiw, liw = uiw, ui, li, err='y', ylim=NULL,
           xlim=NULL, type="p",  col=par("col"), barcol=col,
           pt.bg = par("bg"),  sfrac = 0.01, gap=1, lwd=par("lwd"),
           lty=par("lty"), labels=FALSE, add=FALSE, xlab, ylab,  minbar,
           maxbar, ... )

### Arguments

`x,y` | coordinates for the center of error bars. `y` defaults to `1:n`.
`uiw` | width of the upper or right error bar. Set to `NULL` or `NA` to omit upper bars.
`liw` | width of the lower or left error bar. Defaults to same value as `uiw`. Set to `NULL` or `NA` to omit lower bars.
`ui` | upper end of error bars. Defaults to `y + uiw` or `x + uiw` depeding on `err`. Set to `NULL` or `NA` to omit upper bars.
`li` | lower end of error bars. Defaults to `y - liw` or `x - liw` depedning on `err`. Set to `NULL` or `NA` to omit lower bars.
`err` | direction for error bars. Set to "y" for vertical bars. Set to "x" for horizontal bars. Defaults to "y".
`col` | color of plotting character used center marker of error bars. Default is "black".
`xlim, ylim` | range of x/y values to include in the plotting area.
`type` | point/line type; passed to `points`
`barcol` | color of the error bars. Defaults to the same value as `col`
`pt.bg` | background color of points (use `pch=21, pt.bg=par("bg")` to get open points superimposed on error bars).
`sfrac` | width of "crossbar" at the end of error bar as a fraction of the x plotting region. Defaults to 0.01.
`gap` | space left between the center of the error bar and the lines marking the error bar in units of the height (width) of the letter "O". Defaults to 1.0
`lwd` | width of bar lines.
`lty` | line type of bar lines.
`labels` | either a logical value indicating whether the circles representing the x values should be replaced with text giving the actual values or a vector containing labels to use instead. Defaults to `FALSE`.
`add` | logical indicating whether error bars should be added to the current plot. If `FALSE` (the defailt), a new plot will be created and symbols/labels for the x values will be plotted before drawing error bars.
`minbar` | minumum allowed value for bar ends. If specified, values smaller than `minbar` will be replaced with `minbar`.
`maxbar` | maximum allowed value for bar ends. If specified, values larger than `maxbar` will be replaced with `maxbar`.
`...` | optional plotting parameters
`xlab` | label for x axis.
`ylab` | label for y axis.

### Author(s)

Original version by Bill Venables wvenable@attunga.stats.adelaide.edu.au posted to r-help on Sep. 20, 1997. Enhanced version posted to r-help by Ben Bolker ben@zoo.ufl.edu on Apr. 16, 2001. This version was modified and extended by Gregory R. Warnes greg@warnes.net. Additional changes suggested by Martin Maechler maechler@stat.math.ethz.ch integrated on July 29, 2004.

### See Also

`plotmeans` provides an enhanced wrapper to `plotCI`.

### Examples

      # plot means and
      data(state)
      tmp   <- split(state.area, state.region)
      means <- sapply(tmp, mean)
      stdev <- sqrt(sapply(tmp, var))
      n     <- sapply(tmp,length)
      ciw   <- qt(0.975, n) * stdev / sqrt(n)

      # plain
      plotCI(x=means, uiw=ciw)

      # prettier
      plotCI(x=means, uiw=ciw, col="black", barcol="blue", lwd=1)

      # give mean values
      plotCI(x=means, uiw=ciw, col="black", barcol="blue",
             labels=round(means,-3), xaxt="n", xlim=c(0,5) )
      axis(side=1, at=1:4, labels=names(tmp), cex=0.7)

      # better yet, just use plotmeans ... #
      plotmeans( state.area ~ state.region )

[Package gplots version 3.0.1 Index]