plot-methods {flexmix} | R Documentation

## Rootogram of Posterior Probabilities

### Description

The `plot` method for `flexmix-class` objects gives a rootogram or histogram of the posterior probabilities.

### Usage

    ## S4 method for signature 'flexmix, missing':
    plot(x, y, mark=NULL, markcol=NULL,
      col = NULL, eps=1e-4, root=TRUE, ylim=TRUE, main=NULL, xlab="",
      ylab="", as.table=TRUE, endpoints=c(-0.04, 1.04),...)

### Arguments

`x` | An object of class `"flexmix"`.
`y` | Not used.
`mark` | Integer: mark posteriors of this component.
`markcol` | Color used for marking components.
`col` | Color used for the bars.
`eps` | Posteriors smaller than `eps` are ignored.
`root` | If `TRUE`, a rootogram of the posterior probabilities is drawn, otherwise a standard histogram.
`ylim` | A logical value or a numeric vector of length 2. If `TRUE`, the y axes of all rootograms are aligned to have the same limits, if `FALSE` each y axis is scaled separately. If a numeric vector is specified it is used as usual.
`main` | Main title of the plot.
`xlab` | Label of x-axis.
`ylab` | Label of y-axis.
`as.table` | Logical that controls the order in which panels should be plotted: if 'FALSE' (the default), panels are drawn left to right, bottom to top (as in a graph); if 'TRUE', left to right, top to bottom.
`endpoints` | Vector of length 2 indicating the range of x-values that is to be covered by the histogram. This applies only when 'breaks' is unspecified. In 'do.breaks', this specifies the interval that is to be divided up.
`...` | Further graphical parameters for the lattice function histogram.

### Details

For each mixture component a rootogram or histogram of the posterior probabilities of all observations is drawn. Rootograms are very similar to histograms, the only difference is that the height of the bars correspond to square roots of counts rather than the counts themselves, hence low counts are more visible and peaks less emphasized. Please note that the y-axis denotes the number of observations in each bar in any case.

Usually in each component a lot of observations have posteriors close to zero, resulting in a high count for the corresponding bin in the rootogram which obscures the information in the other bins. To avoid this problem, all probabilities with a posterior below `eps` are ignored.

A peak at probability one indicates that a mixture component is well seperated from the other components, while no peak at one and/or significant mass in the middle of the unit interval indicates overlap with other components.

### Author(s)

Friedrich Leisch and Bettina Gruen

### References

Friedrich Leisch. FlexMix: A general framework for finite mixture models and latent class regression in R. Journal of Statistical Software, 11(8), 2004. http://www.jstatsoft.org/v11/i08/

Jeremy Tantrum, Alejandro Murua and Werner Stuetzle. Assessment and pruning of hierarchical model based clustering. Proceedings of the 9th ACM SIGKDD international conference on Knowledge Discovery and Data Mining, pages 197-205. ACM Press, New York, NY, USA, 2003.

Friedrich Leisch. Exploring the structure of mixture model components. In Jaromir Antoch, editor, Compstat 2004 - Proceedings in Computational Statistics, pages 1405-1412. Physika Verlag, Heidelberg, Germany, 2004. ISBN 3-7908-1554-3.

[Package flexmix version 2.2-4 Index]