The Science

SSI has enjoyed long and successful associations with and the intellectual guidance of the leading academic minds in statistical and methodological research.

R.D. Bock

Dr. R. Darrell Bock did his graduate study at the University of Chicago, and taught at the University of Chicago from 1955-1958 before moving on to the University of North Carolina where he taught from 1958 – 1964. In 1964 he returned to the University of Chicago, where he is a current Professor Emeritus at the Department of Psychology.

He served as president of the Psychometric Society from 1972-1973, and has received the National Council on Measurement in Education award for “Contributions to the design and analysis of educational assessment” in 1990, the Educational Testing Service award for “Distinguished contributions to educational measurement” in 1991, the American Psychological Association Division 5 award for “Distinguished lifetime contributions to evaluation, measurement, and statistics in 1997, and the American Educational Research Association Linquist Award for distinguished contributions to educational measurements in 1999. Dr Bock has authored over 70 books and articles.

Stephen du Toit

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. He is a Fellow of the South African Statistical Association and a member of the 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.

Robert D Gibbons

Robert D. Gibbons is the Blum-Riese Professor and a Pritzker Scholar at the University of Chicago. He has appointments in the Departments of Medicine, Public Health Sciences and Comparative Human Development. He also directs the Center for Health Statistics.

Professor Gibbons is a Fellow of the American Statistical Association, the International Statistical Institute, and the Royal Statistical Society, and a member of the National Academy of Medicine of the National Academy of Sciences. He has authored more than 300 peer-reviewed scientific papers and five books. His statistical work spans the areas of longitudinal data analysis, item response theory, environmental statistics and drug safety and has led to thousands of applications in the biological and social sciences. Professor Gibbons has received life-time achievement awards from the American Statistical Association, the American Public Health Association and Harvard University. He is a founder of the Mental Health Statistics section of the American Statistical Association. He is an author of SuperMix.

Don Hedeker

Donald Hedeker’s chief expertise is in the development and use of advanced statistical methods for clustered and longitudinal data, with particular emphasis on mixed-effects models. He is the primary author of several freeware computer programs for mixed-effects analysis. With Robert Gibbons, he is the author of the text “Longitudinal Data Analysis,” published by Wiley in 2006. More recently, he has developed methods and software for analysis of intensive longitudinal data, which are data with many measurements over time, often collected using mobile devices and/or the internet. Such data are increasingly obtained by researchers in many research areas, for example in the areas of mobile health (mHealth) and ecological momentary assessment (EMA) studies. He is an associate editor for Statistics in Medicine and Journal of Statistical Software. He is an author of SuperMix.

Karl Jöreskog

Karl G Jöreskog is Professor Emeritus at Uppsala University in Sweden. He was born in Åmål, Sweden 1935 and did his undergraduate studies at Uppsala University in 1955-1957, with a major in Mathematics and Physics. He received a PhD in Statistics at Uppsala University 1963 with a dissertation entitled Statistical Estimation in Factor Analysis: A New Technique and Its Foundation, a topic suggested to him by Professor Herman Wold. He was a Research Statistician at Educational Testing Service and a Visiting Professor at Princeton University 1964-1971. During these years he published several papers in Psychometrika on the method of maximum likelihood applied to exploratory and confirmatory factor analysis, covariance structure analysis, and multiple group factor analysis. These papers laid the foundation for the LISREL model which was presented for the first time at the conference Structural Equation Models in the Social Sciences held at Madison Wisconsin in November 1970.

In 1971 Jöreskog returned to Sweden to become Professor of Statistics at Uppsala University. In 1984 he was appointed a Research Professor of Multivariate Statistical Analysis, a position he held until his retirement in 2000.

Jöreskog has received three Doctors honoris causa (Honorary Doctors): By the Faculty of Economics and Statistics at the University of Padua, Italy, 1993, by the Norwegian School of Economics, Bergen, Norway, 1996, and by the Faculty of Psychology at the Friedrich-Schiller- Universität, Jena, Germany, 2004. He became Honorary Professor at Tianjin University of Finance and Economics, Tianjin, China in 2006. Jöreskog is a member of the Swedish Royal Academy of Sciences, a Fellow of the American Statistical Association, and an Honorary Fellow of the Royal Statistical Society. He served as President of Psychometric Society in 1977-78 and organized the first European Psychometric Society Meeting in Uppsala 1978.

Robert Mislevy

Robert Mislevy holds the Frederic M. Lord Chair in Measurement and Statistics at Educational Testing Service. He is also Emeritus Professor of Measurement, Statistics, and Evaluation (EDMS) at the University of Maryland, College Park, with affiliations in Second Language Acquisition and the Joint Program in Survey Methods. He earned his Ph.D. in Methodology of Behavioral Research at the University of Chicago in 1981. Mislevy’s research interests center on applying recent developments in statistical methodology and cognitive research to practical problems in educational assessment. His work has included a multiple-imputation approach for integrating sampling and test-theoretic models in the National Assessment of Educational Progress (NAEP), a Bayesian inference network for updating the student model in an intelligent tutoring system, and an evidence-centered design framework for assessment. He is an author of BILOG-MG. He has recently published books on Bayesian Networks in Educational Assessment, Bayesian Psychometric Modeling, and Sociocognitive Foundations of Educational Measurement. 

Among his honors and awards is the American Educational Research Association’s Raymond B. Cattell Early Career Award for Programmatic Research, the National Council of Measurement in Education’s Award for Technical Contributions to Educational Measurement (three times), AERA’s Lindquist Award, and the International Language Testing Association’s Samuel J. Messick Memorial Lecture Award. In 1992, he was elected president of the Psychometric Society. In 2003, he was presented the National Council of Measurement’s Award for Career Contributions to Educational Measurement.

Eiji Muraki

After graduating from Waseda University in 1972, dr. Muraki acquired his Ph.D. in measurements, evaluation and statistical analysis programs from the University of Chicago in 1983. After graduating, he worked on the development of psychological statistic models used in educational assessments such as the California Education Measurement Project at the National Opinion Research Center (NORC).

As a senior researcher, he worked on statistics and quantitative psychological research at the Educational Testing Service (ETS) from 1989, and worked at ACT in 2001, and has since 2002 been professor at the Graduate School of Educational Informatics Research Division, Tohoku University. His main field of research is quantitative psychology and the development of methods used in educational measurements. He has published many scientific papers, and developed the computer program PARSCALE. Has made an enthusiastic contribution to the development of quantitative psychology in Japan and the U.S. through various academic society activities. Dr.Muraki received the Japanese Association for Research on Testing (JART) award in 2010.

Stephen Raudenbush

Stephen Raudenbush is the Lewis-Sebring Distinguished Service Professor in the Department of Sociology, the College and the Harris School of Public Policy Studies and Chairman of the Committee on Education at the University of Chicago. He is interested in statistical models for child and youth development within social settings such as classrooms, schools, and neighborhoods. He is best known for his work developing hierarchical linear models and the HLM program, with broad applications in the design and analysis of longitudinal and multilevel research. he is currently studying the development of literacy and math skills in early childhood with implications for instruction; and methods for assessing school and classroom quality.

He is a member of the National Academy of Sciences, the American Academy of Arts and Sciences, the recipient of the American Educational Research Association award for Distinguished Contributions to Educational Research.

David M. Thissen

David Thissen is professor of quantitative psychology at the University of North Carolina and former President of the Psychometric Society. Upon receiving his PhD in 1976, Thissen joined the psychology faculty at the University of Kansas and was appointed an associate professor (with tenure) five years later. He moved to the University of North Carolina at Chapel Hill in 1990 as a full professor of psychology and served as the chair of the L. L. Thurstone Psychometric Laboratory until 2002. He continues to serve UNC as a full professor in the Department of Psychology and Neuroscience.

He is a fellow at the American Statistical Association and the American Psychological Society. He is known for his contributions to item response theory. He is the author of hundreds of publications on testing and measurement, patient-reported health outcomes (PROs), human development, and statistical graphics.] He published Test Scoring with Howard Wainer in 2001. He has also developed numerous psychometric software programs including Multilog and IRTPRO.

Michele Zimowski

Michele F. Zimowski is a Senior Survey Methodologist in the Department of Statistics and Methodology at NORC. In that role, she oversees the design, measurement, and statistical data analysis components of specific projects and serves as a consultant in those areas on other projects. Zimowski has more than 25 years of practical experience in the design and analysis of large-scale surveys, and in the development and application of item-response-theoretic (IRT) methods to educational, vocational, and behavioral data.  

Zimowski is author or co-author of numerous articles and reports in the areas of survey methodology, measurement, and education. Her published work covers a broad range of topics–from reporting and reducing non-response in travel surveys to applications of full-information factor analysis to the successes and challenges of college-going minority youth. She has presented papers at the annual meetings of a number of professional organizations including the American Educational Research Association, the Psychometric Society, the National Council of Measurement in Education, and the American Association for Public Opinion Research. Zimowski is also the first author of the BILOG-MG program. Over the years, she has participated in numerous sessions to train other professionals in IRT methodology and analysis.