R is a free software environment for statistical computing and graphics, which is similar to the S language. R provides a wide variety of statistical (linear and nonlinear modelling, classical statistical tests, time-series analysis, classification, clustering, ...) and graphical techniques, and is highly extensible. One of R's strengths is the ease with which well-designed publication-quality plots can be produced, including mathematical symbols and formulae where needed. Furthermore, R is available for Windows, Linux and Mac OS X and can be downloaded from www.r-project.org.