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A Cross Sectional Analysis of the Excess Comovement of Stock Returns

Robin M. Greenwood

Harvard Business School - Finance Unit; National Bureau of Economic Research (NBER)

March 2005

HBS Finance Research Paper No. 05-069

In the presence of limits to arbitrage, cross-sectional variation in periodic investor demand should be related to the degree of comovement of returns. I exploit the unusual weighting system of the Nikkei 225 index in Japan to identify cross-sectional variation in periodic demand for index stocks. Relative to their weights in a value weighted index, some stocks in the Nikkei are overweighted by a factor of ten or more. Using overweighting as an instrument for the proportionality between demand shocks for index stocks, I find a strong positive relation between overweighting and the comovement of a stock with other stocks in the index, and a negative relationship between index overweighting and comovement with stocks outside of the index. Put simply, overweighted stocks have high betas. The results suggest that excess comovement of stock returns is a consequence of an institutionalized commonality in trading behavior, rather than inefficiencies related to the speed at which index stocks incorporate economy-wide information.

Number of Pages in PDF File: 47

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Date posted: April 9, 2005  

Suggested Citation

Greenwood, Robin M., A Cross Sectional Analysis of the Excess Comovement of Stock Returns (March 2005). HBS Finance Research Paper No. 05-069. Available at SSRN: https://ssrn.com/abstract=698162 or http://dx.doi.org/10.2139/ssrn.698162

Contact Information

Robin M. Greenwood (Contact Author)
Harvard Business School - Finance Unit ( email )
Boston, MA 02163
United States
617-495-6979 (Phone)
National Bureau of Economic Research (NBER)
1050 Massachusetts Avenue
Cambridge, MA 02138
United States
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