and for the package versions available in November 2006 when this review was conducted, two packages, MicrOsiris and Epi Info, could read files with blanks for missing. Two other programs, Stat4U and WinIdams need something for the missing, like -9 or -9.99. The other packages could only handle data sets with no missing values. The more recent review, from 2022, compared output from a number of free to use statistical packages and found they all gave pretty much the same results. In contrast, there are various reviews of commercial statistical software, such as a comparison between several major packages and a brief review of several packages. Using free statistical software Before using any statistical packages, it is generally a good idea to have a solid background in Statistics. Then the packages can be used to the best advantage, for example, to choose the most appropriate test, to make sure all the necessary assumptions are met, so that the appropriate conclusions can be drawn. Once the statistical issues are understood, the next step is to decide which package to use. Most of these packages are menu driven, and can be learned in a couple of hours at most, except R, which is generally code driven and requires a much longer time to learn, and to some extent CDC's Epi Info, which also takes some time to learn. Several of the packages also have tutorials. These tutorials help with a basic introduction and learning the basics of the programs. For example, CDC has tutorials about Epi Info. The CDC page also lists a video slide show tutorial from the University of Nebraska, and another site has online training classes. R has a large number of tutorials and manuals, in English and other languages and a faq site. PSPP has a particularly easy to follow tutorial, and a rich set of statistical analyses, including T-test, Oneway and Factorial Anova, Linear and Logistic regression and Principal components analysis. It also has provision for it to be very easy to import data from many other different file formats. A few of the packages have email discussion lists, including R and PSPP. Most of the packages have online manuals, guides or help pages. These are useful when there are questions about specific procedures or statistical tests. Some manuals or guides are for R, PSPP, and Zelig. The CDC EpiInfo site itself does not have a manual,