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Welcome to SSI Live™
Started by prominent researchers, including Professor R Darrell Bock, SSI has been developing, publishing, and distributing specialized statistical software products since 1971. SSI has been a driving force behind many widely used statistical software packages, which includes HLM and SuperMix for multilevel modeling; BILOG-MG, PARSCALE, and later IRTPRO that enabled item response theory modeling applications in large-scale educational assessments as well as in psychological and behavioral measurement; and LISREL, the very progenitor of structural equation modeling.
In early 2020, Vector Psychometric Group, LLC (VPG), a North Carolina-based software and consulting company, completed the acquisition of SSI. VPG is well-known for its leadership in the patient-centered clinical outcome research space, as well as its high-end statistical software offerings, including flexMIRT®, the industry-leading multilevel and multidimensional item analysis and test scoring software that support many large-scale assessment programs in the US and beyond. Jointly VPG and SSI provide nearly 60 years of statistical software development experience.
With your SSI Live™ subscription, you are entitled to many more benefits in comparison to previous SSI software licensing models. Click here to view a side-by-side comparison chart of features, including exclusive educator benefits. Selected 14-day SSI Live™ Trial subscription remains freely available for a potential user’s evaluation purposes of the Commercial Licenses. Please reach out to [email protected] for more details
We understand that the end-users’ institutions may have additional regulatory and compliance requirements that necessitate changes to the end-user license agreement. Additional fees will be assessed if changes are proposed to cover the cost of negotiations.
Currently we offer no native Mac version of any of our programs currently available. However, if you have a dual-boot set-up or a Windows emulator, any of our programs should run without issues as long as your hardware is not using Apple’s proprietary ARM-based chips because of known compatibility issues. Note that we can only provide support for using the software and are unable to provide guidance on setting up a Mac to allow for a program to be usable. Parallels Desktop is the most frequently used of the emulators. VirtualBox is a free alternative from Oracle, but it can be very slow compared to Parallels.
IRTPRO™ - Commercial
LISREL Academic
HLM Academic
flexMIRT™
flexMIRT™ is software specifically designed for the analysis of item response data, such as what can be obtained from a quality of life measure, attitude survey, or academic test. It is able to accommodate a wide variety of IRT models to factor structures that are both unidimensional and multidimensional (e.g., the items measure more than one concept). flexMIRT™ provides a wide variety of item and model fit statistics and indices for evaluating results and produces several different types of IRT-based scores, depending on user request. While flexMIRT™ is primarily a confirmatory modeling program, it has capabilities for performing EFA with analytic rotations as well.
IRTPRO™
IRTPRO™ is an advanced application for item calibration and test scoring using item response theory (IRT). It comes with an intuitive graphical user interface and offers built-in production quality IRT graphics. Suitable for educators, students, researchers, and assessment organizations, IRTPRO™ has become increasingly popular in the educational, psychological, social, and health sciences. IRTPRO™ handles any combination of unidimensional or multidimensional versions of popular IRT models, in multiple groups. The users may choose from a number of sophisticated estimation algorithms for item and person parameters. User-defined parameter restrictions and the availability of many test statistics facilitate statistical inference for IRT modeling.
HLM
HLM provides statistical tools for comprehensive hierarchical data modeling. A recent addition to this popular program is the option to estimate an HLM from incomplete data, using a completely automated approach that generates and analyses multiply imputed data sets from incomplete data.
LISREL
LISREL provides tools for structural equation modeling, data manipulations and basic statistical analyses, hierarchical and non-linear modeling, generalized linear modeling, and generalized linear modeling for multilevel data.
SUPERMIX
SuperMix is an application for comprehensive mixed-effect modeling and combines the functionality of four mixed-effects programs, MIXREG, MIXOR, MIXNO, and MIXPREG into a single application to provide estimates for mixed-effects regression models.
BILOG-MG
BILOG-MG is an extension of BILOG that is designed for the efficient analysis of binary items, including multiple-choice or short-answer items scored right, wrong, omitted, or not-presented. BILOG-MG is capable of large-scale production applications with unlimited numbers of items or respondents.
PARSCALE
PARSCALE implements Item Response Theory (IRT) measurement methods for binary, multiple-category and rating-scale items. The flexibility and the wealth of information provided by this program have kept it in regular use by researchers around the world.
AUXAL
Auxal performs both structural and nonstructural auxological analysis of human growth in standing height or recumbent length.