I recently had the opportunity to take an interest in Eugène Fama's work on the theory of market efficiency. It is a theory where markets are categorized into three types: the weak form efficiency, the semi-strong form efficiency and the strong form efficiency. A week form efficiency market represents a market where share prices reflect all the information contained in the price history, so it will be impossible to obtain abnormal returns by building strategies based on the price history. A semi-strong efficiency market reveals that share prices reflect only public information and not "internal information". Finally, a "perfect market" or a market of strong form efficiency is a market where share prices reflect all available information, both public and private. In this last form of efficiency, it therefore becomes impossible to make profits other than by chance since it is impossible to predict future prices. However, after reading this theory, I wondered whet...