NBER Working Paper No. 12785
---- Acknowledgements ----
This paper has been prepared as a draft chapter for the Handbook of Economics and Information Systems, Terrence Hendershott, ed., Elsevier Science, 2006. We thank David Caballero and Jason McCoy for their research assistance. Axel Ockenfels gratefully acknowledges support from the German Science Foundation (DFG). David Reiley gratefully acknowledges support from NSF grant SES-0094800. The views expressed herein are those of the author(s) and do not necessarily reflect the views of the National Bureau of Economic Research.