**Two nice R libraries (October 14, 2005)**.

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I found a couple of nice libraries in R available from CRAN (Comprehensive R Achive Network). The first, vcd, was recommended by a regular contributor to the epidemio-l list. This library provides visualization techniques with special emphasis on categorical data. There is a nice function to draw a series of odds ratios and confidence intervals, for example, and very simple code to produce a mosaic plot. A more thorough description of vcd is available at

According to the description, the functions in vcd were inspired by the book

**Visualizing Categorical Data**. Michael Friendly, Cary, NC: SAS Publishing. [BookFinder4U link]

which I do not have in my library, but which sounds like a very interesting book.

I found the second library, epitools, when I went searching on the web for resources to calculate an exact confidence interval for a Poisson rate. In addition to the exact Poisson intervals, the package can perform age standardization, draw epidemic curves, and has a variety of useful utility functions and interesting data sets. The description of epitools is available at

and the authors maintain a site for this library and other free software at