Value-Added to What? How a Ceiling in the Testing Instrument Influences Value-Added Estimation
Value-added measures of teacher quality may be sensitive to the quantitative properties of the student tests upon which they are based. This paper focuses on the sensitivity of value-added to test-score-ceiling effects. Test-score ceilings are increasingly common in testing instruments across the country as education policy continues to emphasize proficiency-based reform. Encouragingly, we show that over a wide range of test-score-ceiling severity, teachers' value-added estimates are only negligibly influenced by ceiling effects. However, as ceiling conditions approach those found in minimum-competency testing environments, value-added results are significantly altered. We suggest a simple statistical check for ceiling effects.
The authors thank Andrew Zau and many administrators at San Diego Unified School District, in particular Karen Bachofer and Peter Bell, for helpful conversations and assistance with data issues. We also thank Yixiao Sun, Julie Cullen, Nora Gordon and Dale Ballou for their useful comments and suggestions, and the Spencer Foundation and the National Center for Performance Incentives for research support. The underlying project that provided the data for this study has been funded by a number of organizations including The William and Flora Hewlett Foundation, the Public Policy Institute of California, The Bill and Melinda Gates Foundation, the Atlantic Philanthropies and the Girard Foundation. None of these entities has funded the specific research described here, but we warmly acknowledge their contributions to the work needed to create the database underlying the research. The views expressed herein are those of the author(s) and do not necessarily reflect the views of the National Bureau of Economic Research.
Cory Koedel & Julian Betts, 2010. "Value Added to What? How a Ceiling in the Testing Instrument Influences Value-Added Estimation," Education Finance and Policy, MIT Press, vol. 5(1), pages 54-81, January. citation courtesy of