This study analyzes the performance of stocks listed on Bovespa - the São Paulo Stock Exchange - between 03/17/1998 and 08/03/2004. First, stationarity was tested in order to check whether these stocks followed the random walk model. The results showed that all returns were stationary. In relation to prices, 90% of all stock prices revealed a unit root, that is, they followed the random walk model at level. The other 10% were rarely traded. These findings suggest that the Brazilian stock market is efficient in its weak form. Then, the efficiency of the Brazilian market in its semi-strong form was also tested in terms of the firm's size, by estimating a conditional CAPM. The traditional proxy used to measure a firm's size is the market value. However, other size proxies like book value and profit were also used. The results revealed that, independently of the proxy used, no size portfolio was capable of obtaining systematically abnormal returns. Finally, a significant correlation was found between beta and size only when book value is used as a size proxy. Nevertheless, its coefficients were low and their signals were inconsistent. In general terms, these results suggest that the Brazilian market is also efficient in its semi-strong form.
Size Effect; CAPM; Efficient Capital Markets; Market Anomaly
