In the mood to trade? Weather may influence institutional investors' stock decisions

The researchers conclude that cloudier days increase the perception that individual stocks and the Dow Jones Industrials are overpriced, increasing the inclination for institutions to sell.

The research paper, "Weather-Induced Mood, Institutional Investors, and Stock Returns," has been published in the January 2015 issue of The Review of Financial Studies. The research was collaborated by Case Western Reserve University's Dasol Kim and three other finance professors (William Goetzmann of Yale University, Alok Kumar of University of Miami and Qin Wang of University of Michigan-Dearborn).

Institutional investors represent large organizations, such as banks, mutual funds, labor union funds and finance or insurance companies that make substantial investments in stocks. Kim said the results of the study are surprising, given that professional investors are well regarded for their financial sophistication.

"We focus on institutional investors because of the important role they have in how stock prices are formed in the markets," said Kim, assistant professor of banking and finance at Case Western Reserve's Weatherhead School of Management. "Other studies have already shown that ordinary retail investors are susceptible to psychological biases in their investment decisions. Trying to evaluate similar questions for institutional investors is challenging, because relevant data is hard to come by."

Building on previous findings from psychological studies about the effect of sunshine on mood, the researchers wanted to learn how mood affects professional investor opinions on their stock market investments.

By linking responses to a survey of investors from the Yale Investor Behavior Project of Nobel Prize-winning economist Robert Shiller and institutional stock trade data with historical weather data from the National Oceanic and Atmospheric Administration, the researchers concluded aggregated data shows that seasonably sunnier weather leads to optimistic responses and a willingness to buy.

The research accounts for differences in weather across regions of the country and seasons. They show that these documented mood effects also influence stock prices, and that the observed impact does not persist for long periods of time.

A summary of the research was also recently featured at The Harvard Law School Forum on Corporate Governance and Financial Regulation.