Thanks to event-studies, it is possible to measure value creation for firms implied in a takeover as well as their competitors. Horizontal operations create more value than others. However, it is difficult to determine the origin of the gain: the increase in the share value may have different sources. In some cases, the market seems to anticipate an improvement in productive efficiency, in others an increase in market power.
CHARLETY-LEPERS, P. (2005). Le temps et la valeur des entreprises : le cas des offres publiques. Problèmes économiques, pp. 46-48.