Scientific Software International was incorporated in the State of Michigan in December 1971 and commenced business in April 1972. According to its charter, the purpose of the corporation is to publish software in the scientific and technical fields. It enters into marketing agreements with program authors, edits, typesets and prints program manuals and related documents created by the authors. It prepares the programs for distribution to customers and adapts the programs to a variety of computers and operating systems. It advertises, packages, and markets the programs, manuals and books. The authors are paid a royalty on all revenues from these activities.
In 2001, after Prof. Darrell Bock (SSI's co-founder and long-time President) retired from active involvement with the company, SSI instituted an Academic Advisory Board to assist management with its long term goals.
For its customers, the corporation offers a variety of services. Registered program users may call on the company technical support line if they encounter problems in operating the programs. From time to time, the company presents two- or three-day training sessions in the application of the programs to research problems. Usually, the program authors are instructors in these sessions, which are typically coordinated with meetings of professional organizations such as the American Statistical Association, American Psychological Association, or the American Educational Research Association. Participants pay to attend these sessions and receive company publications as part of their tuition. The number of sessions has averaged three a year since the company was formed.
Nowadays, these sessions are promoted through the company's website, groupmail to the customer database, and postings to the relevant discussion lists on the Internet.
In addition, ads for the programs are placed from time to time in journals such as the American Statistician, the American Psychologist, Educational Researcher, the American Journal of Marketing, etc.
Originally the programs were distributed on lease for mainframe computers, later Unix workstations. Although these annual renewable leases are still a small source of income, emphasis has shifted completely to versions of the programs for personal computers. With this development, much more emphasis has been placed on each program user's interface, the online helpfile, and the preparation and editing of the computer manuals, which must be more detailed for PC users who are working independently. The company retains editorial and typesetting experts to produce high quality manuals.
The company has distribution arrangements with software publishers in the USA and abroad.
The company's first important product was MULTIVARIANCE, by Professor Jeremy Finn, State University of New York at Buffalo. The program performs univariate and multivariate analysis of variance for any design up to ten factors, and gives exact solutions in both unbalanced and balanced designs. It includes analysis of covariance, discriminant analysis, canonical analysis, repeated measures analysis, and Potthoff-Roy analysis of longitudinal data. The program was leased to several hundred mainframe sites during the 70's, but declined in popularity after similar programs were included in the SSI and SAS systems during the 80's. Recently, however, it has had a new lease on life as a PC program that is faster, more detailed, and more convenient than its competitors. In January 2003, it will be released as a Windows program.
The second main area of program application has been item analysis and test scoring, which has a large market in the educational field. The most important of these programs is BILOG, written by Robert Mislevy, University of Maryland, and Darrell Bock, University of Chicago. The program performs modern item-response theoretic analysis of tests consisting of binary (right-wrong) scored items.
BILOG-MG, by Michele Zimowski (National Opinion Research Center), Eiji Muraki (Tohoku University), Robert Mislevy (University of Maryland), and Darrell Bock (University of Chicago), is a multiple-group variation of the BILOG program. As such, it can do everything BILOG does, but it is also designed to detect and estimate item parameter drift and differential item functioning (DIF).
Another program in this field is MULTILOG, by Professor David Thissen, University of North Carolina at Chapel Hill. The program performs a similar analysis as BILOG on rating scales and items scored in ordered categories. PARSCALE, written by Eiji Muraki, Tohoku University, and Darrell Bock, University of Chicago, serves similar purposes for large-scale analysis.
The final program in this area is TESTFACT, by Douglas Wilson and Robert Wood, University of London Examinations Council, and Professor Robert Gibbons, University of Illinois, Chicago. This program performs classical test scoring, item analysis, and item factor analysis.
These IRT based programs are among the most advanced psychometric procedures now available and are enjoying increasing use. They will all be available as Windows programs in January, 2003.
At present, the company's most widely-used programs, and main source of revenue, are the structural equation modeling programs PRELIS and LISREL of Professors Karl Jöreskog and Dag Sörbom, University of Uppsala. These are the most advanced programs available for analysis of large linear systems when both dependent and independent variables are subject to error, and/or when qualitative variables are included in the analysis. The programs also perform path analysis, multiple indicator-multiple criterion analysis, recursive and nonrecursive modeling of temporal data, confirmatory factor analysis, and analysis of covariance structures. With the latest releases (versions 8.30 and 8.50), a huge number of features and improvements have been added, as can be seen elsewhere on this website.
Another important program marketed by SSI is HLM -- a program for analysis of multistage sampling designs under the hierarchical linear model, by Professor Anthony Bryk, University of Chicago, Professor Stephen Raudenbush, University of Michigan, and Richard Congdon, Harvard University. It is available for Windows, DOS, and several Unix platforms.
The AUXAL program, by Darrell Bock (University of Chicago), Stephen du Toit (SSI), and David Thissen (University of North Carolina) performs auxological analysis of longitudinal measurements of human stature.