Stephen du Toit is Director of Software Development at VPG. Previously, he held the position of Vice President at Scientific Software International, Inc. from 2004 until 2015 and President until the end of 2019. He received his PhD in Mathematics and Statistics from the University of South Africa. He is a recipient of the University of Pretoria medal for outstanding achievement in research (1990) and the P.M. Robbertse medal for outstanding contribution towards research at the Human Sciences Research Council of South Africa (1985).
Stephen has worked on several statistical software packages such as LISREL, a program for fitting structural equation models, and IRTPRO, a program for fitting unidimensional and multidimensional IRT models. Further examples are SuperMix, a program for multilevel modeling of continuous and categorical outcomes, and Auxal, a program for the prediction of human growth. In addition to his involvement in the technology field, he held the position of adjunct professor in the department of Psychology at the University of North Carolina and currently holds the position of professor emeritus in the Department of Statistics at the University of Pretoria, South Africa. Before moving to the USA, he was invited by the Universities of Chicago and Stanford to participate in research projects and to teach. He is a Fellow of the South African Statistical Association and a member of the American Psychometric Society.
He has reviewed technical papers for several journals including Psychometrika, Multivariate Behavioral Research, and Structural Equation Modeling. Dr. du Toit was the PI on over $5 million in funded SBIR projects. He is co-author of two books and has contributed to several book chapters and numerous peer-reviewed journals. His publications cover topics on optimization techniques, repeated measurements, structured means and covariances, nonlinear growth models, graphical display of data, and vector time series processes.