PSPP seems to correspond only to SPSS base. The only downside I can see, though, is with the statement “no additional packages to purchase in order to get ‘advanced’ functions.” That appears to be because there aren’t any advanced functions. You can use PSPP with its graphical interface or the more traditional syntax commands. Its backend is designed to perform its analyses as fast as possible, regardless of the size of the input data. PSPP can perform descriptive statistics, T-tests, linear regression and non-parametric tests. There are no additional packages to purchase in order to get “advanced” functions all functionality that PSPP currently supports is in the core package. Neither are there any artificial limits on the number of cases or variables which you can use. The most important of these exceptions are, that there are no “time bombs” your copy of PSPP will not “expire” or deliberately stop working in the future.

It is a Free replacement for the proprietary program SPSS, and appears very similar to it with a few exceptions. This is the description from its website:

I have not tried it yet, but it does look promising. I just heard recently about PSPP, which is a free, open source version of SPSS.

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