David R. Lemmon is a Research Associate at The Methodology Center in The Pennsylvania State University's College of Health and Human Development. He holds a PhD in Mechanical Engineering from the University of Cincinnati. His areas of previous work include finite element analysis, automobile crash simulation, and biomechanical modeling of the diabetic foot. Since 2001, he has served as the Center's Senior Statistical Programmer, managing the creation of new statistical software for research and education.

Joseph L. Schafer Associate Professor in the Department of Statistics at The Pennsylvania State University and a Principal Investigator at The Methodology Center. He holds a PhD in Statistics from Harvard University. His areas of research include statistical methods for missing values, analysis of longitudinal data, statistical computing and methodology for studies of substance-use prevention. He has served as a statistical consultant to numerous government agencies and has taught many workshops and short courses on topics related to missing data.