“…Depending on the type of information, announcements increase or decrease the value of stocks on the market. Quintessentially, it involves estimating the direction and size of the abnormal return attributable to unanticipated information, see further Pham (2015), Chi and Tang (2008), Hall and Kenjegaliev (2009), Campbell et al (1997), McWilliams and Siegel (1997), Corrado and Zivney (1992), Corrado (1989), Ball and Tourus (1988), Warner (1980, 1985) and Dyckman et al (1984). In this paper an event date is upgrade or downgrade announcement made by three rating agencies.…”