IRTPRO

For many years SSI has had a widely distributed suite of four IRT (Item Response Theory) programs called Bilog-MG, Multilog, Parscale and Testfact. However, with growth and success also come new users and new expectations. Despite their success, these IRT programs are far from perfect measured by today's software standards. Furthermore, they share a great deal of similarities and overlapping functionalities. Thus, it became evident that a single, state-of-the-art software product must be developed to replace these four programs.
　

In an effort to meet the growing demands of our user community, SSI has developed a new software product, called IRTPRO, which is on the cutting edge of current technology. The program has been tested extensively on the Microsoft Windows platform with Windows7, Vista and XP operating systems. Important sections of the IRTPRO numeric engine have been parallelized to run on multiple cores simultaneously.

IRTPRO supports both model-based and data-based graphical displays. Model-based graphs, currently available for unidimensional IRT models only, are trace lines, information curves, combined trace lines-information curves, total information, and test characteristic curves.

IRTPRO imports data from a variety of statistical software packages as well as importing data from fixed format data (.fixed), comma-separated (.csv), tab-delimited (usually .txt), and Excel (.xls) files. Whatever the original format, the imported data are saved to an IRTPRO data file with extension .ssig that is displayed visually as a spreadsheet, similar in appearance to an Excel spreadsheet.

BILOG-MG
Graphical user interface
Efficient analysis of binary items including multiple choice or short-answer items scored right, wrong, omitted, or not-presented
Capable of large scale production analysis, and handling of multiple groups
Performs item analysis and scoring of any number of subtests or subscales
Non-equivalent groups equating
Vertical equating of test forms
Differential item functioning (DIF)
Detection and correction for parameter trends over time (DRIFT)
Calibration and Scoring of tests in two-stage testing procedures
Estimation of latent ability or proficiency distributions
Provision for items inserted in tests to estimate item statistics, but not included in calculation of examinee scores ("variant items")
Item fit statistics, theoretical and empirical reliability
Information curves and reliabilities for putative test forms
Presentation quality IRT graphics, can be imported in Word, Access, etc.
Detailed online HELP documentation includes description of interface, syntax, and examples.
　

PARSCALE

The flexibility and the wealth of information provided by this program have kept it in regular use by researchers around the world
One, two, and three-parameter logistic models
Samejima's model for graded responses
Master's partial credit model
Generalized partial credit model
Analysis of rating scale items such as open-ended essay questions
Analysis of multiple-choice items
Differential item functioning (DIF)
Analysis of mixtures of item types
Rater's-effect analysis
Multiple-group polytomous item response models
Presentation quality IRT graphics, can be imported in Word, Access, etc.
Detailed online HELP documentation includes syntax and examples.
　

TESTFACT

Marginal maximum likelihood (MML) exploratory factor analysis and classical item analysis of binary data
Computes tetrachoric correlations, principal factor solution, classical item descriptive statistics, fractile tables and plots
Handles up to 10 factors using numerical quadrature: up to 5 for non-adaptive and up to 10 for adaptive quadrature
Handles up to 15 factors using Monte Carlo integration techniques
Varimax (orthogonal) and PROMAX (oblique) rotation of factor loadings
Handles an important form of confirmatory factor analysis known as "bifactor" analysis: Factor pattern consists of one main factor plus group factors Simulation of responses to items based on user specified parameters
Correction for guessing and not-reached items
Allows imposition of constraints on item parameter estimates
Handles omitted and not-presented items
Detailed online HELP documentation includes syntax and annotated examples.