Vector Psychometric Group (VPG) is proud to offer cutting-edge software for web-based data collection and item response data analysis. Authored by Li Cai, one of the leading experts in psychometrics, Adaptest®, IRTPRO™, and flexMIRT™ have state-of-the-art features unavailable in other programs. Adaptest®, our web-based computerized adaptive testing (CAT) engine, has been updated to a “plug-in,” allowing any existing electronic data collection system (EDC) to administer adaptive tests and provide real-time scoring with minimal modifications. IRTPRO™, with its intuitive graphical user interface, built-in data management capacity, high quality graphics, and a professional HTML-based output delivery system, have become widely adopted by educators, researchers, and assessment professionals. flexMIRT™, VPG’s flagship IRT software, has some of the richest psychometric and statistical features defining the state of the art. With the ability to be installed and called remotely, flexMIRT™ is ideal for the individual analyses of an applied researcher or the large-scale analyses and scoring needed for operational use.


Adaptest® from VPG allows research teams to use a range of outcome measures from single-item responses to the most advanced item response theory-based assessments.  Adaptest® is easy to implement from full integration in the host system to a simple JavaScript plugin.  Adaptest® can run on any Microsoft or Linux system and easily scales on the Amazon Elastic beanstalk.  Regardless of the method, Adaptest® is able to easily integrate into most existing EDC systems, allowing them to administer items adaptively, if desired, and provide real-time scoring with minimal programming changes.


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. To purchase a flexMIRT™ subscription, please visit


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. To purchase a IRTPRO™ subscription, please visit

SSI Statistical Programs

We are happy to announce that in early 2020, Scientific Software International Inc. (SSI), has become a wholly owned subsidiary of Vector Psychometric Group, LLC. All of SSI’s statistical programs has been migrated to a new subscription-based software delivery and support model called SSI Live™.

Customized Software

VPG also offers clients the opportunity to customize Adaptest® or flexMIRT™, creating software that is built to meet your specific needs. Please contact us at for more information about how Adaptest® and flexMIRT™ can be put to work for you.


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.