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The number and quality of free statistical software offerings appears to be increasing. Here are two interesting sites that offer good quality software for free.

**Item Response Theory macros**. Hardouin
J-B. Accessed on 2005-09-15.

[Excerpt]

IRT (Item Response Theory) has been undergoing important developments in the past few years. Indeed, many general purpose statistical packages still don't have procedures implementing these new indices, methods and models. As a consequence, a significant number of specific packages have been developed by psychometricians (see http://www.assess.com). However, no package offers a comprehensive set of methods, and no package has emerged as standard tool in the field. The increasing sophistication of general statistical packages, on the other hand, allows user-written routines to be developed which will implement IRT methods within the context of an already-familiar computing environment. This site presents a set of macro-programs for use with Stata or SAS. While they were originally developed to analyse quality of life scales, they can, of course, be used in the area of psychometrics, test construction etc.anaqol.free.fr

**Mx**. Neale M. Accessed on 2005-09-15.

[Excerpt] Mx is a combination of a matrix algebra interpreter and a numerical optimizer. It enables exploration of matrix algebra through a variety of operations and functions. There are many built-in fit fuctions to enable structural equation modeling and other types of statistical modeling of data. It offers the fitting fuctions found in commercial software such as LISREL, LISCOMP, EQS and CALIS, along with facilities for maximum likelihood estimation of parameters from missing data structures, under normal theory. Complex 'nonstandard' models are easy to specify. For further general applicability, it allows the user to define their own fit functions, and optimization may be performed subject to linear and nonlinear equality or boundary constraints.www.vcu.edu/mx