Herd Behavior Analysis in Tehran Stock Exchange with Chiang and Zheng Model

Behavioral finance, as a sub-field of behavioral economics, has posed many challenges to classic financial theories and market efficiency. In general, herd behavior emerges when investors decide to follow other investors rather than relying on their own analysis and knowledge and change their decisions based on other investors’ opinions. Even though this behavior may be rational for less sophisticated investors, the existence of wide herding may result in volatility in returns and instability of the capital market, which is known as a source of financial risk. The purpose of this study is to investigate the herd behavior among investors in Tehran Stock Exchange during the 4-year period from 23/05/2015 to 21/05/2019.

This study examines the existence of wide herding among investors in Tehran Stock Exchange by using the Chiang and Zheng model which is an econometric model based on the daily return of sectors, the daily return of the selected portfolio and cross-sectional absolute deviation. Besides, Chiang and Zheng model is the only econometric based model which can detect herd behavior in up-markets and down-markets separately.

The findings of the study clearly illustrate that the assumption of investors herd behavior in the market has been confirmed. In addition, herd behavior is stronger in the up-markets than the down-markets during the mentioned 4-year period. It should be noted that herd behavior was detected in both up- markets and down- markets, but the intensity was higher in up-markets.

With respect to the obtained coefficients in the regression equations and the type of herd behavior in terms of occurring in down markets or up markets, it can be concluded that investors in Tehran Stock Exchange are generally affected by herd behavior, but in periods of market decline, investors decide and act somewhat more rational, and they show lower intensity of herd behavior in their investments.