Inference in Long-Horizon Event Studies: A Bayesian Approach with Application to Initial Public Offerings

Statistical inference in long-horizon event studies has been hampered by the fact that abnormal returns are neither normally distributed nor independent. This study presents a new approach to inference that overcomes these difficulties and dominates other popular testing methods. I illustrate the use of the methodology by examining the long-horizon returns of initial public offerings (IPOs). I find that the Fama and French (1993) three-factor model is inconsistent with the observed long-horizon price performance of these IPOs, whereas a characteristic-based model cannot be rejected.     

Improved Methods for Tests of Long-Run Abnormal Stock Returns

We analyze tests for long-run abnormal returns and document that two approaches yield well-specified test statistics in random samples. The first uses a traditional event study framework and buy-and-hold abnormal returns calculated using carefully constructed reference portfolios. Inference is based on either a skewness-adjusted t -statistic or the empirically generated distribution of long-run abnormal returns. The second approach is based on calculation of mean monthly abnormal returns using calendar-time portfolios and a time-series t -statistic. Though both approaches perform well in random samples, misspecification in nonrandom samples is pervasive. Thus, analysis of long-run abnormal returns is treacherous.     

股票送转、异常收益和管理层持股比例

中国股市的股票送股、转增(以下简称"送转")往往能够带来异常收益,本文使用事件研究的方法和1999年到2010年的股票送转相关的数据,在同、异方差的假设、按照送转比例和现金红利比例划分不同子样本以及考虑到信息提前泄露而重新定义事件日的情况下,一致的发现了异常收益①的存在,而现金红利会减少送转事件带来的异常收益。本文进一步探究这种异常收益的来源,发现管理层的持股比例会正向显著地影响异常收益,并且这种影响在一系列稳健性检验下依然存在。本文还使用了工具变量,因此克服了可能存在的管理层持股比例的内生性问题。     

Short-term under/overreaction, anticipation or uncertainty avoidance? Evidence from India

We examine the short-term price behaviour of three, size-conditioned Indian stock market indices, in response to informational shocks. A standard mean-adjusted returns model as well as the GJR-GARCH specification point towards underreaction to negative events in the medium and small capitalization indices. Also, the pre-event coefficients are generally negative and statistically significant, regardless of the sign of the shock, thus ruling out information leaks. We uncover a stable abnormal volatility pattern which increases monotonically a few days before the shock before suddenly decreasing in magnitude on the event day and beyond. We suggest uncertainty avoidance as a potential explanation of these features. The results are fairly robust across alternative event selection procedures, time, and size-conditioned shocks.     

Nonparametric rank tests for event studies

Because stock prices are not normally distributed, the power of nonparametric rank tests dominate parametric tests in event study analyses of abnormal returns on a single day. However, problems arise in the application of nonparametric tests to multiple day analyses of cumulative abnormal returns (CARs) that have caused researchers to normally rely upon parametric tests. In an effort to overcome this shortfall, this paper proposes a generalized rank (GRANK) testing procedure that can be used on both single day and cumulative abnormal returns. Asymptotic distributions of the associated test statistics are derived, and their empirical properties are studied with simulations of CRSP returns. The results show that the proposed GRANK procedure outperforms previous rank tests of CARs and is robust to abnormal return serial correlation and event-induced volatility. Moreover, the GRANK procedure exhibits superior empirical power relative to popular parametric tests.     

The impact of hedging on the market value of equity

We examine the annual stock performance of firms that disclose the use of derivatives to hedge over the period 1995 to 1999. We find that only 21.6% of publicly traded U.S. corporations in our sample hedged with derivative instruments over this period and their use is concentrated in the larger companies. Similar to other studies we find that when derivatives are used, interest rate and currency securities are used much more frequently than commodity products. Our sample of 1308 companies that hedge outperforms other securities by 4.3% per year on average over our sample period. This result is robust to several alternative methods of estimating abnormal returns. When we segment performance by the type of hedge used, however, we find that the over-performance is due entirely to larger firms that hedge currency. We find no abnormal returns for firms hedging either interest rates or commodities. The abnormal returns in firms hedging currency is robust to alternative models that seek to control for exchange rate fluctuations and global equity returns; however, we find no significant abnormal returns to currency hedgers when using an augmented model that controls for the role of intangible assets.     

事件模拟与非正常收益模型的检验力——基于中国A股市场的经验检验

本文分别以1990年12月至2003年12月两市所有A股公司为抽样总体,检验了均值调整模型、市场调整模型和市场模型为基础的多种检验方法的检验力。研究发现,无论事件研究中各公司事件是否相近或重叠,都应采用市场模型为基础的非参数秩检验法。而累积非正常收益的检验也应以市场模型为计算基础。若样本公司事件日相近或重叠,统计量的设置要考虑累积非正常收益截面数据的相关性。均值调整模型在本文所定义的各种检验方法中,均无明显优势。经敏感性测试,本文结论不变。     

The Long‐run Performance Following Dividend Initiations and Resumptions: Underreaction or Product of Chance?

We examine the long-term stock performance following dividend initiations and resumptions from 1927 to 1998. We show that postannouncement abnormal returns are significantly positive for equally weighted calendar time portfolios, but become insignificant when the portfolios are value weighted. Moreover, the equally weighted results are not robust across subsamples. We also document postannouncement reductions in the risk factor loadings of underlying stocks. Cross-sectionally, these reductions are negatively related to the contemporaneous price drifts, suggesting the price drifts may be a sample-specific result of chance. Our results underscore the importance of testing for changes in risk loadings in future long-term event studies.     

Short-term overreaction to specific events: Evidence from an emerging market

This paper investigates the short-term overreaction to specific events and whether stock prices are predictable in the Egyptian stock exchange (EGX). We find evidence of the short-term overreaction in the EGX. Losers (“bad news” portfolios) significantly outperform winners (“good news” portfolios) and investors can earn abnormal return by selling the winners and buying losers. Terrorist attacks have negative and significant abnormal returns for three days post event followed by price reversals on day four post event. Whereas, the tensions in the Middle East region have a negative and significant abnormal returns on event day followed by price reversals on day one post event. Moreover, the formation of a new government has no effect on the average abnormal returns post event in the EGX. The results also show that small firms tend to have greater price reversals compared to large firms. Overall, our results provide evidence of the leakage of information in the EGX.     

Individual Investor Trading and Return Patterns around Earnings Announcements

This paper provides evidence of informed trading by individual investors around earnings announcements using a unique data set of NYSE stocks. We show that intense aggregate individual investor buying (selling) predicts large positive (negative) abnormal returns on and after earnings announcement dates. We decompose abnormal returns following the event into information and liquidity provision components, and show that about half of the returns can be attributed to private information. We also find that individuals trade in both return‐contrarian and news‐contrarian manners after earnings announcements. The latter behavior has the potential to slow the adjustment of prices to earnings news.     

A股与H股市场的差异与互动

本文选择了28家既在香港发行H股,又在内地发行A股的上市公司作为样本,研究分割市场之间的差异性和互动关系.通过对比相同上市公司在两个市场上的收益性和波动性差异,本文发现:两个市场在年报公告、中报公告、季报公告以及预告事件下获得的超额收益具有显著差异,而在分红通过公告事件下未产生显著差异;同时,除了分红通过公告(旧信息)事件未引起市场产生明显的波动以外,其余事件都对两个市场产生了显著的波动性影响.另外,我们也发现"H股引起A股变化"的可能性要大于"A股引起H股变化"的可能性.     

Individuals’ Trading Prior to Earnings Announcements

This paper investigates the relationship between individuals’ net trading and stock price movements before and after annual earnings announcements for the Taiwan Stock Exchange. We conduct an event study on the effects of pre‐event individual trade imbalances on pre‐ and post‐announcement abnormal returns. With a unique and comprehensive dataset, we accurately classify executed orders by aggressiveness of order price. The evidence indicates that while individuals, as a group, are not informed about impending earnings announcements, individuals who place aggressive orders are informed as their net trading coincides with contemporaneous and future stock returns. Aggressive individuals lose their edge during the financial crisis. More importantly, the advantage (disadvantage) for individuals who adopt aggressive (passive) orders weakens when foreign institutions own concentrated equity in firms. We also find that net individual trading contains information about abnormal returns that either past returns or volume does not subsume. Controlling for past returns, trading volume and volatility, or using an alternative measure of net individual trading does not change our conclusions.     

Abnormal Returns in the Acquisition Market: The Case of Bank Holding Companies, 1990–1993

Recent evidence suggests that announcements of bank holding company acquisitions result in wealth transfers from the bidding to target shareholders. Empirically, this is demonstrated through findings of negative average abnormal returns to bank holding company acquirers and positive average abnormal returns to targets on announcement. Using a sample of acquisitions from the early 1990s—a period marked by the removal of significant geographic entry barriers—this paper reexamines the issue by applying a general statistical model to the event study framework to more precisely measure abnormal returns. In particular, we model returns according to the GARCH process to control for time-varying volatility. With respect to the unconditional distributions of acquirer and target abnormal returns, our findings are consistent with prior research. Further investigation into the conditional distribution of acquirer returns finds that, on announcement, interstate acquisitions using the purchase method of accounting actually increased shareholder wealth for acquirers (on average) by 1.44%. However, over a longer event horizon, the most important determinants of acquirer abnormal returns appear to be the relative size of the transaction and the method of accounting.     

Endogenous Events and Long-Run Returns

We analyze event abnormal returns when returns predict events.In fixed samples, we show that the expected abnormal returnis negative and becomes more negative as the holding periodincreases. Asymptotically, abnormal returns converge to zeroprovided that the process of the number of events is stationary.Nonstationarity in the process of the number of events is neededto generate a large negative bias. We present theory and simulationsfor the specific case of a lognormal model to characterize themagnitude of the small-sample bias. We illustrate the theoryby analyzing long-term returns after initial public offerings(IPOs) and seasoned equity offerings (SEOs).     

Firm characteristics and long-run stock returns after corporate events

The well-documented abnormal long-run buy-and-hold returns to firms issuing equity in initial public offerings and seasoned equity offerings, firms bidding in mergers, and firms initiating dividends can be attributed to imperfect control-firm matching. In addition to firm size and market-to-book ratio, event firms on average differ from control firms in terms of idiosyncratic volatility, liquidity, return momentum, and capital investment, each of which also explains returns. We propose a simple regression-based approach to control for differences in firm characteristics across event and control firms, and we show that long-run abnormal returns do not differ significantly from zero for event firms in the 1980 to 2005 period. The returns to event firms are, therefore, consistent with patterns known to exist for the broad stock market and do not require event-specific explanations.     

Wealth effects of convertible-bond and warrant-bond offerings: a meta-analysis

The literature on wealth effects associated with the announcements of convertible-bond and warrant-bond offerings is reviewed. The findings of 35 event studies, which include 84 sub-samples and 6310 announcements, are analysed using meta-analysis. We find a mean cumulative abnormal return of?1.14% for convertibles compared with?0.02% for warrant bonds, the significant difference confirming a relative advantage for warrant bonds. Abnormal returns for hybrid securities issued in the USA are significantly more negative than those issued in other countries. In addition, issuing hybrid securities to refund debt does not seem to be favoured by investors. Finally, several factors identified as important by theory or in prior research are not significant within our cross-study models, suggesting that more evidence is needed to confirm whether they are robust.     

The January effect for individual corporate bonds

We examine the presence, magnitude and determinants of a January effect for individual corporate bonds. Our results provide empirical evidence of positive and statistically (but not economically) significant abnormal returns in January across different event windows and models. Our results suggest that, in the addition to the term and default factors, the excess stock returns, size and book-to-market factors are priced for individual bond returns. We investigate a number of determinants of the January abnormal returns for individual bonds. Our findings suggest that the reversal and tax-loss selling effects are important determinants of the abnormal returns on individual bonds.     

An Empirical Analysis of the Stockholder-Bondholder Conflict in Corporate Spin-Offs

We analyze the effect of daily stock and bond abnormal returns around spin-off announcements. Over a three-day event window, we find statistically significant abnormal returns of 3.07% for stocks and 0.11% for straight bonds. Both stock and bond abnormal returns are higher for firms with lower interest and dividend payouts. Stock abnormal returns are also higher for firms with higher pre-spin-off leverage. Overall, we find that the firm value increase compensates for the wealth transfer effect and that bondholders' wealth is not reduced as a result of spin-off.     

EXTENSIONS OF THE STANDARDIZED CROSS‐SECTIONAL APPROACH TO SHORT‐HORIZON EVENT STUDIES

Strong evidence indicates that short‐horizon event‐induced abnormal returns and volatility vary significantly over event days. Event‐study methods that assume constant event‐induced abnormal returns and volatility over event days have potentially inflated Type I error rates and poor test power. Our simple extensions of the Boehmer, Musumeci, and Poulsen (1991) approach scale abnormal returns with conditional variance, which is estimated with GARCH(1,1) and an indicator of the event in a two‐stage estimation. Our method improves the Boehmer, Musumeci, and Poulsen approach on model specification and test power, even under challenging event‐induced mean and volatility structures, and could standardize short‐horizon event studies.     

PRICE AND VOLUME EFFECTS ASSOCIATED WITH THE CREATION OF STANDARD & POOR'S MIDCAP INDEX

In this paper we explore price and volume effects associated with the 1991 creation of Standard & Poor's MidCap 400 index. Prior work on changes in the composition of existing indices finds a significant price response to the announcement. Various authors link the effect to price pressure, information, an outwardly shifting demand curve for securities, and the increased attention that comes with inclusion in an index. Using event study methodology, we find significant price and volume effects during the two weeks leading up to the Standard & Poor's announcement, but no significant effect in the two-day interval around the event. Apparently, information leakage and/or anticipation preceded the creation of the index. The price run-up is permanent since the positive abnormal returns leading up through the announcement are not associated with significantly negative abnormal returns after the announcement. In addition, MidCap stocks significantly outperform the market during the fifty-two weeks following the announcement. Using cross-sectional regressions, we show that these prior-period abnormal returns are positively related to abnormal volume and institutional holdings. We also find that firms trading over-the-counter had larger price run-ups than NYSE or AMEX firms.