Trading Patterns and Excess Comovement of Stock Returns Author(s): Robin M. Greenwood and Nathan Sosner Source: Financial Analysts Journal , Sep. - Oct., 2007, Vol. 63, No. 5 (Sep. - Oct., 2007), pp. 69-81 Published by: Taylor & Francis, Ltd. Stable URL: https://www.jstor.org/stable/4480877 JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact
[email protected]. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms Taylor & Francis, Ltd. is collaborating with JSTOR to digitize, preserve and extend access to Financial Analysts Journal This content downloaded from 206.253.207.235 on Thu, 03 Dec 2020 18:55:42 UTC All use subject to https://about.jstor.org/terms Financial Analysts Jou rnal Volume 63 . Number 5 FM ?2007, CFA Institute Trading Patterns and Excess Comovement of Stock Returns Robin M. Greenwood and Nathan Sosner In April 2000, 30 stocks were replaced in the Nikkei 225 Index. The unusually broad index redefinition allowedfor a study of the effects of index-linked trading on the excess comovement of stock returns. A large increase occurred in the correlation of trading volume of stocks added to the index with the volume of stocks that remained in the index, and opposite results occurredfor the deletions. Daily index return betas of the additions rose by an average of 0.45; index return betas of the deleted stocksfell by an average of 0.