Adhesion and migration to the differentiated levels of corporate governance: an investigation of the event window

Even though many researchers use event study methodology, these studies commonly diverge in terms of the length of window considered and of findings. The definition of the event window is essential, but it always involves a certain degree of subjectivity and arbitrariness. In order to establish objective bases for delimiting the event window, a methodology is proposed based on the results of analysis of 75 cases of companies that have adhered or migrated to the differentiated levels of corporate governance (NDGC) of BM&FBovespa. These results reveal the great importance of small event windows, because in 47 cases out of 75 windows of five trading sessions before and five after the event (5-5) were observed. This indicates that the use of large event windows to capture and measure the effects of adhesion or migration to the NDGC, although frequent, may be misleading.