Jonathan Weeks is a senior measurement scientist in the Research & Development division at ETS. He holds a Ph.D. in research and evaluation methodology from the University of Colorado at Boulder, an M.A. in educational psychology from the University of Colorado at Denver, and a B.A. in English from Colorado College. His primary research interest is in the area of test equating and linking with a focus on unidimensional and multidimensional vertical scaling and issues surrounding construct shift. He has worked on a wide range of projects in which he has contributed to psychometric, statistical, and design elements. This work includes scaling and validation efforts for large-scale international assessments (Programme for International Student Assessment, Programme for the International Assessment of Adult Competencies, and Trends in International Mathematics and Science Study); a set of measures focused on foundational reading skills and scenario-based assessment; and a battery of general fluid reasoning measures; among others. He also developed and maintains an R package for IRT-based linking methods. Weeks has expertise in latent variable models, unidimensional and multidimensional item response theory, automated test assembly, and adaptive and multistage measurement designs. He has authored and coauthored numerous grant proposals that have been funded, collectively, at over six million dollars. Additionally, he has published in various peer-reviewed journals including the Journal of Educational and Behavioral Statistics, Educational Measurement: Issues and Practices, and the Journal of Statistical Software.