Niels G. Waller, Ph.D., is Full Professor and Director of Quantitative/Psychometric Methods and Professor of Individual Differences, Personality and Behavioral Genetics in the Department of Psychology at the University of Minnesota, Twin Cities. He received the 1999 American Psychological Association Distinguished Scientific Award for Early Career Contribution to Psychology in the area of Individual Differences, a 1997 Raymond B. Cattell Award for Multivariate Experimental Research, Society for Multivariate Experimental Psychology, a 1997 Morton Prince Award, International Society for the Study of Dissociation, and a 1989 Thomas Small Prize: Harvard University. Dr. Waller obtained his Ph.D. from the University of Minnesota and completed his clinical internship at the Minneapolis VA Medical Center. He is currently an Editor of Applied Psychological Measurement and serves on the editorial board of numerous journals. His primary research interests include the development and evaluation of Quantitative Models of Individual Differences; Scale Development and Models of Person-Item Interactions in Personality/Psychopathology Assessment (Item Response Theory, Adaptive Testing); Taxometrics, Factor Analysis and Structural Equation Modeling; Psychometric Theory; and Genetic and Environmental Models of the Development and Expression of Psychopathology, Personality, Social Attitudes and Beliefs.