SAS™ (SAS Institute, 2009) and R (R development core team, 2009) are two statistical software packages used in many fields of research. SAS is commercial software developed by SAS Institute; it includes well-validated statistical algorithms. It can be licensed but not purchased. Paying for a license entitles the licensee to professional customer support. However, licensing is expensive and SAS sometimes incorporates new statistical methods only after a significant lag. In contrast, R is free, open-source software, developed by a l arge group of people, many of whom are volunteers. It has a large and growing user and developer base. Methodologists often release applications for general use in R shortly after they have been introduced into the literature. Professional customer support is not provided, though there are many resources for users. There are settings in which one of these useful tools is needed, and users who have spent many hours gaining expertise in the other often find it frustrating to make the transition.