Paul D. Allison, Ph.D., is Professor of Sociology at the University of Pennsylvania. He received his Ph.D. in sociology from the University of Wisconsin in 1976 and did postdoctoral study in statistics at the University of Chicago and the University of Pennsylvania. He has published three books and more than 25 articles on statistical methods in the social sciences. These have dealt with a wide variety of methods including linear regression, log-linear analysis, logit analysis, probit analysis, measurement error, inequality measures, missing data, Markov processes, and event history analysis. At present, his research is focused on the analysis of longitudinal data, especially with determining the causes and consequences of events. Each summer, he teaches 5-day workshops on event history analysis and categorical data analysis that draw nearly 100 researchers from around the US. At Penn, he teaches graduate courses on event history analysis, categorical data analysis, and structural equation models with latent variables. His substantive interests include scientists' careers and theories of altruistic behaviour.