Maria Rosa Borges

Efficient market hypothesis in European stock markets

This paper reports the results of tests on the weak-form market efficiency applied to stock market indexes of UK, France, Germany, Spain, Greece and Portugal, from January 1993 to December 2007. We use a runs test, and joint variance ratio tests, which are performed using daily and weekly data for the period 1993–2007 and for a subset, 2003–2007. Daily and weekly returns are not normally distributed, because they are negatively skewed and leptokurtic, and also display conditional heteroscedasticity. Overall, we find mixed evidence on the efficient market hypothesis (EMH). The hypothesis is rejected on daily data for Portugal and Greece, due to first-order positive autocorrelation in the returns. However, the empirical tests show that these two countries have been approaching a martingale behavior after 2003. France and UK data rejects EMH, due to the presence of mean reversion in weekly data, and stronger in recent years. Taken together, the tests for Germany and Spain do not allow the rejection of EMH, this last market being the most efficient.

Random Walk Tests for the Lisbon Stock Market

This article reports the results of tests on the weak-form market efficiency applied to the PSI-20 index prices of the Lisbon stock market from January 1993 to December 2006. As an emerging stock market, it is unlikely that it is fully information-efficient, but we show that the level of weak-form efficiency has increased in recent years. We use a serial correlation test, a runs test, an Augmented Dickey–Fuller (ADF) test and the multiple variance ratio test proposed by Lo and MacKinlay (1988) for the hypothesis that the stock market index follows a random walk. Nontrading or infrequent trading is not an issue because the PSI-20 includes only the 20 most traded shares. The tests are performed using daily, weekly and monthly returns for the whole period and for five sub-periods which reflect different trends in the market. We find mixed evidence, but on the whole, our results show that the Portuguese stock market index has been approaching a random walk behaviour since 2000, with a decrease in the serial dependence of returns.

Abnormal returns before acquisition announcements: evidence from Europe

Acquisition announcements influence the stock price of target firms, providing an opportunity for insiders to obtain significant abnormal returns. We study the presence of positive abnormal returns before the announcement date, in target firms, quoted in Euronext markets (Belgium, France, The Netherlands and Portugal) from 2001 to 2007. We investigate whether the pre-announcement run-up of prices can be explained by rumours in the media and the percentage of capital previously owned by the bidding firm, among other factors. We examine cumulative abnormal returns in an event window of 60 days prior the acquisition announcement, with the event date adjusted for the previous disclosure of news about the acquisition, in the media. We compute a run-up index, and find that there are abnormal positive returns before the announcement date, confirming previous studies. We find that a significant part of the run-up is explained by: (i) market anticipation triggered by legitimate sources of information, namely, rumours in the media about the possibility of an acquisition bid and (ii) the percentage of capital previously owned in the target firm, by the bidding firm.

A model of stock price adjustment after dividends

Purpose - The purpose of this paper is to discuss the stock price adjustment after a dividend distribution, allowing for different types of investors and market imperfections, including taxes and transaction costs. Design/methodology/approach - An arbitrage model is developed to determine the possible equilibria for the stock price adjustment, after a dividend distribution. The approach is theoretical, providing general results. Findings - The model shows that, in the presence of different types of investors, a unique equilibrium only exists in the absence of transaction costs. The allowance for market imperfections, such as taxes and transactions costs, implies that there is not a unique equilibrium for the level of stock price adjustment following a dividend distribution event, but rather there is much possible equilibrium. It is showed that the observation of abnormal trading volume around the dividend event may give us some insights on the identification of which investors are present in the market. Practical implications - On future studies of the stock price adjustment after dividend distributions, it should be taken into account that there is no unique equilibrium. Originality/value - The main contribution of this paper is to show that the existence of taxes and transaction costs precludes the determination of a unique equilibrium point for the stock price adjustment after a dividend distribution.