Announcing the release of SuperMix

A new version of the SuperMix program is immediately available.

Use of Stat/Transfer Version 15

The data import feature has been upgraded from Stat/Transfer Version 14 to the most recently released Version 15 to ensure import/export compatibility with software packages such as SPSS, SAS and STATA. Among others, Stat/Transfer supports importing data from the most current SAS, SPSS, STATA, MINITAB, MATLAB and R software.

Dynamic link libraries

Executables have been replaced with 32bit and 64bit dynamic link libraries. The GUI determines if the computer uses a 64bit or 32bit processor.

Announcing the release of PARSCALE 5

A new version of the PARSCALE program is immediately available.

New features

  1. The number of examinees in a dataset has been increased from 1 million to ten million.
  2. The maximum length of all file names has been changed from 128 to 256 characters. This “feature” is only useful if the DLL can handle syntax file with directory. Currently the UI break the full path into <drive>/<dir> and <filename>, change the current working directory to <drive>/<dir> and call the BLM.exe with <filename> (together with other parameters).
  3. The phases can be run in batch mode

VPG Releases New Version of IRTPRO

SSI’s parent company, Vector Psychometric Group, LLC, released IRTPRO 5.

IRTPRO™ is an application for comprehensive item calibration and test scoring using IRT models. IRTPRO™ was first released in 2010.  The current version of IRTPRO™ is Version 5.0 (released date: June 17, 2020).

As of June 17, 2020, IRTPRO™ is no longer marketed by SSI.  Instead, SSI’s parent company, Vector Psychometric Group, LLC, is exclusively marketing IRTPRO™ under a subscription-based software delivery and support model.  Please visit the updated online store at to purchase a subscription or to manage your IRTPRO license. 

IRT models for which item calibration and scoring are implemented in IRTPRO™ are based on unidimensional and multidimensional [confirmatory factor analysis (CFA) or exploratory factor analysis (EFA)] versions of the widely used response functions such as 1PL, 2PL, 3PL, graded, generalized partial credit, and nominal.  More information about IRTPRO™ can be found at

All questions about IRTPRO™ sales should be directed to  Feel free to continue to write to if you have any technical questions about IRTPRO™ (Version 2 – Version 4). IRTPRO™ 5+ users should write to the new, dedicated IRTPRO™ customer support desk at

HLM 8 Now Available on SSI Live™

HLM transitions to the SSI Live™ software-as-subscription service.

We are pleased to announce that after several years of development, SSI is offering a brand new HLM software licensing, delivery, and support model. We call it SSI Live™. HLM is the first program to transition to the new model. SSI Live™ is a subscription, similar to the popular rental licenses that we used to market, but with many more features.With your renewable SSI Live subscription, you are entitled to many more benefits in comparison to previous licensing models.  Click here to view a side-by-side comparison chart of features.

The following subscriptions are available:

Standard subscriptions for 3, 6 or 12 months:

This subscription is a standard non-commercial, academic, and educational copy of HLM. While your renewable subscription is active, key benefits include: 

  • download and simultaneously install state-of-the-art HLM program on two (2) computers  
  • additional installs can be purchased and added at any time at discount
  • free access to all upgrades or updates 
  • free software support and technical support 
  • additional discounts on subscriptions of other SSI or VPG programs 

Basic subscriptions for 3 or 12 months:

This subscription is a basic non-commercial, academic, and educational copy of HLM. While your renewable subscription is active, you are entitled to the following benefits: 

  • download and install state-of-the-art HLM program on one computer  
  • free access to all upgrades or updates 

Trial version:

  • A fully-functioning 14-day trial subscription is available for a potential user’s evaluation purposes.  
  • For educators who plan to use HLM in instruction, your students may be eligible access the full version of HLM for free during your course or workshop. 

To acquire a subscription or to find out more about SSI Live™, please visit For help on registering, see our Quickstart guide. For more information on adding additional users to a license, see our FAQ on this topic

Current users with perpetual licenses will be able to continue to use the program according to the terms of the end user license agreement. Over time, this transition will impact on the technical support we offer our users who hold older perpetual licenses. 

HLM 8 users:

Please refer to an email recently sent from sharing more details on how to activate your subscription account. 

HLM 6 users:

As you are aware, the final release of HLM 6 occurred in 2009, which is more than a decade ago.  The current release of HLM is Version 8. Software products built on older operating systems and third-party components become increasingly more difficult to maintain and support, and as a consequence, also less secure.  Due to such concerns, we will phase out support for HLM 6 at the end of this calendar year (12/31/2020).  Because you have a perpetual license, you certainly may continue to use the program according to the terms of the end user license agreement beyond this year.  However, as of January 1, 2021, our HLM Support Desk will not respond to HLM 6 inquiries. 

SSI Acquired by Vector Psychometric Group

Scientific Software International Inc. is acquired by Vector Psychometric Group.

We are happy to announce that in early 2020, Scientific Software International Inc., became a wholly owned subsidiary of Vector Psychometric Group, LLC, a North Carolina-based software and consulting company. We believe this exciting new development in SSI’s corporate history will reinvigorate the SSI products that have for so long formed the backbone of research in a variety of fields.

An important part of this evolution of SSI is the gradual roll-out of a new software delivery and support model for all our programs. We call it SSI Live™

HLM is the first program to transition. After purchasing an SSI Live™ Standard subscription, you will be entitled to:

1) download multiple installs (not possible previously unless with purchasing a special license),

2) free access to all upgrades or updates during the period where the subscription is active,

3) free software support, and

4) discounts on subscriptions to other SSI programs.  

Additional educator benefits are included. Visit SSI Live™ for more information.

Introducing New Features in HLM 8

The HLM8 program has a number of new statistical features.

Estimating HLM from incomplete data

In HLM 8, the ability to estimate an HLM from incomplete data was added. This is a completely automated approach that generates and analyses multiply imputed data sets from incomplete data. The model is fully multivariate and enables the analyst to strengthen imputation through auxiliary variables. This means that the user specifies the HLM; the program automatically searches the data to discover which variables have missing values and then estimates a multivariate hierarchical linear model (”imputation model”) in which all variables having missed values are regressed on all variables having complete data. The program then uses the resulting parameter estimates to generate M imputed data sets, each of which is then analysed in turn. Results are combined using the “Rubin rules”.

Flexible Combinations of Fixed Intercepts and Random Coefficients

Another new feature of HLM 8 is that flexible combinations of Fixed Intercepts and Random Coefficients (FIRC) are now included in HLM2, HLM3, HLM4, HCM2, HCM3 and HLM2.

A concern that can arise in multilevel causal studies is that random effects may be correlated with treatment assignment. For example, suppose that treatments are assigned non-randomly to students who are nested within schools. Estimating a two-level model with random school intercepts will generate bias if the random intercepts are correlated with treatment effects. The conventional strategy is to specify a fixed effects model for schools. However, this approach assumes homogeneous treatment effects, possibly leading to biased estimates of the average treatment effect, incorrect standard errors, and inappropriate interpretation. HLM 8 allows the analyst to combine fixed intercepts with random coefficients in models that address these problems and to facilitate a richer summary including an estimate of the variation of treatment effects and empirical Bayes estimates of unit-specific treatment effects. This approach was proposed in Bloom, Raudenbush, Weiss and Porter (2017).