Rootogram of Posterior Probabilities

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

methods, hplot
## S3 method for class 'flexmix,missing':
plot(x, eps=1e-4, root=TRUE,
  ylim=TRUE, main=NULL, mfrow=NULL, ...)
an object of class "flexmix"
posteriors smaller than eps are ignored
if TRUE, a rootogram of the posterior probabilities is drawn, otherwise a standard historgram
A logical value or a numeric vector of length n2. 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 us
main title of the plot
layout of the plot
further graphical parameters

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.

Usually in each component a lot of observations have posteriors close to zero, resulting in a high count for the corresponing 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.


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 Compstat 2004 -- Proceedings in Computational Statistics, 2004. Accepted for publication.

  • plot-methods
  • plot,flexmix,missing-method
Documentation reproduced from package flexmix, version 0.9-0, License: GPL version 2.

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