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Re: Consistency Index on Cladograms

>In many papers on cladistics, I have noticed that they include a
>consistency index with the cladogram. How is this index calculated, and
>what is it showing that is "consistent"?

The CI is merely a measure of how "cleanly" the data fit the tree.  It's a
simple ratio:  minimum number of character changes possible divided by
minimum number actually observed on the tree.

The CI is of very limited value, and can never be used to compare different
trees from different data sets.  It is highly correlated with data set size
- larger data sets will be noisier - and can therefore only be used as a
comparative metric within the data set.


Christopher Brochu, Ph.D.

Postdoctoral Research Scientist
Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL  60605  USA

phone:  312-922-9410, ext. 469
fax:  312-922-9566