摘要：This research aims to analyze the announcement impact of the 579 act in stock prices in the Brazilian electricity sector. The way the market reacts to information supports investors and assists assets’ analysis and the process of investment portfolio formation. An event study was conducted to assess whether the stocks’ prices and returns have changed after the information was released to the market. The results provided evidence of a semi-strong market efficiency, since prices reacted to the publicly available information, assimilating the new information and then regressing to normality. Specifically, there was, on average, a negative reaction, with a significant drop in prices and stock returns two days after the announcement. However, after the third day, the information was absorbed by the market, and we no longer could detect a negative abnormal returns. Thus, we can conclude that the 579 act was considered a relevant piece of information about the electricity sector, changing stock returns behavior when it was released.
