The Impact of Monetary Policy on Herding Behavior in Tehran Stock Exchange

The experience of the world economy over the last few decades shows that herd behavior is one of the main factors in the formation of financial crises. In identifying the causes of such behavior, economists have pointed the finger of accusation at various factors, and it can be said that monetary policy is at the top of this list. Because of the harmful effects of herd behavior on stock market, identifying the factors influencing this type of behaviour can be of great importance. As a result, the main objective of this study is to investigate the effect of monetary policy on the formation of herd behavior in Tehran Stock Exchange. In this regard, using the monthly data from April 2009 to March 2021 and using the non-linear STR-GARCH model, the effect of monetary policy on the formation of herd behavior in the Iranian stock market was investigated. This method allows the researcher to model the non-linear pattern in herd behavior. In the estimated model, Chang et al.’s index (2000) was used to measure the dispersion of stock returns around the market return, also, the monetary policy variable (growth of liquidity) was used as threshold variable. By choosing this variable as a threshold variable, we can check whether changes in this variable can lead to a transition from a rational regime to a herd regime or not. The results of the study indicate that herd behavior in Tehran Stock Exchange has a variable behavior over time and the linear model is not suitable for investigating such behavior. Also, the results of the research show that based on different values of liquidity growth variable, the behavior of investors changes, so that for monthly liquidity growth values smaller than 2.3%, rational behavior is observed in investment decisions, but with an increase in the growth rate of liquidity and crossing this threshold, over time, herd behavior becomes the dominant behavior in the stock market.