Thesis advisor: Zhijie Xiao / This dissertation covers three essays in the realm of investor heterogeneity. Traditional financial economics theories assume that agents are identical. However, daily practice of finance exhibits phenomena that cannot be explained in the context of homogeneous agents. Thus behavioral economists relax the agent homogeneity assumption and allow different types of agents to interplay, which can explain a series of phenomena, including bubbles (Scheinkman and Xiong, 2003,etc), among others. The first chapter of this dissertation answers the question: what kind of investors flock to an IPO--mostly sophisticated or mostly naive? The answer to this question points to explaining the puzzlingly extreme trading volume on the first day after an IPO. Existing explanations rely on institutions such as day trading, short selling and inter-dealer trades, yet IPO frenzies are common even when these are entirely absent. Recent evidence points to the possible importance of sentiment from retail investors, but it is not yet clear what kind of retail investors might be harboring these emotions. I access a unique data set for Chinese IPOs that measures investor experience and trading records. I find that inexperienced investors are initially drawn to the IPO while established investors remain on the sidelines. Over time, investor composition shifts in favor of experienced investors. More importantly, I identify market timing of purchase (together with the timing of selling, the purchase price, etc, which I define as the decision bundle) as the predominant channel for determining heterogeneity in returns for experienced versus for inexperienced investors. Furthermore, I find that investors do learn to be more patient and get better investment performance thereof. Also, I am able to depict the learning curve by documenting that the marginal effect of learning varies across the level of stock of experience, and across heterogeneous investor type. The second chapter examines the effect of short selling via the unique setting in the Hong Kong stock market and find that, when a stock becomes shortable, its trading activities decrease, liquidities worsen, and information asymmetries increase. This finding contradicts both the existing theoretical models, and recent empirical studies using global financial crisis data. We extend the sequential trading model with short-sales constraints of one asset by Diamond and Verrecchia (1987) to the case of multiple assets. The model predicts that our empirical results are due to uninformed traders switching their tradings to non-shortable securities. Chapter 3 uses a unique short selling setting in Hong Kong stock market, and tests the Chen and Singal (2003) hypothesis that speculative short sellers add to the selling pressure on Mondays and hence add to the weekend effect. We document that, first, the weekend effect exists in Hong Kong stock market, regardless of the existence of short sale constraints; second, after introducing short selling, the individual stocks face more significant weekend effect. The reported result is robust over different estimation models, and over different choices of control groups. Our findings strongly support the Chen and Singal (2003) hypothesis. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.