Matti Keloharju

Aalto University School of Business
P.O.Box 21210, FI-00076 Aalto


NBER Working Papers and Publications

December 2014Common Factors in Return Seasonalities
with Juhani T. Linnainmaa, Peter Nyberg: w20815
A strategy that selects stocks based on their historical same-calendar-month returns earns an average return of 13% per year. We document similar return seasonalities in anomalies, commodities, international stock market indices, and at the daily frequency. The seasonalities overwhelm unconditional differences in expected returns. The correlations between different seasonality strategies are modest, suggesting that they emanate from different common factors. Our results suggest that seasonalities are not a distinct class of anomalies that requires an explanation of its own---rather, they are intertwined with other return anomalies through shared common factors. A theory that is able to explain the risks behind any common factor is thus likely able to explain a part of the seasonalities.
May 2006Sensation Seeking, Overconfidence, and Trading Activity
with Mark Grinblatt: w12223
This study analyzes the role that two psychological attributes%u2014sensation seeking and overconfidence%u2014play in the tendency of investors to trade stocks. Equity trading data are combined with data from an investor%u2019s tax filings, driving record, and psychological profile. We use the data to construct measures of overconfidence and sensation seeking tendencies. Controlling for a host of variables, including wealth, income, age, number of stocks owned, marital status, and occupation, we find that overconfident investors and those investors most prone to sensation seeking trade more frequently.

Published: Mark Grinblatt & Matti Keloharju, 2009. "Sensation Seeking, Overconfidence, and Trading Activity," Journal of Finance, American Finance Association, vol. 64(2), pages 549-578, 04. citation courtesy of

January 2004Interpersonal Effects in Consumption: Evidence from the Automobile Purchases of Neighbors
with Mark Grinblatt, Seppo Ikaheimo: w10226
This study analyzes the automobile purchase behavior of all residents of two Finnish provinces over several years. It finds that a consumer's purchases are strongly influenced by the purchases of his neighbors, particularly purchases in the recent past and by neighbors who are geographically most proximate. There is little evidence that emotional biases, like envy or an urge to conform, lie behind the interpersonal influence in automobile consumption. The most reasonable alternative explanation for these findings is some form of information sharing among neighbors.
January 2002Tax-Loss Trading and Wash Sales
with Mark Grinblatt: w8745
An analysis of trades in the Finnish stock market around the turn of the year shows that Finnish investors tend to realize losses more than gains towards the end of December. They also buy back the same stocks they recently sold, with a repurchase rate that depends on the size of the capital loss and how close the sale is to the end of December. The resulting net buying pressure from these 'wash sale' repurchases is greater for stocks with small market capitalizations and has a calendar pattern that is similar to that of stock returns.

Published: Grinblatt, Mark & Keloharju, Matti, 2004. "Tax-loss trading and wash sales," Journal of Financial Economics, Elsevier, vol. 71(1), pages 51-76, January. citation courtesy of

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