From one perspective, this is puzzling. The IT revolution means that information has become more freely available and more plentiful in the past 20 years. Not only does the internet transmit data instantly, but more information is being generated, such as big data, or computational textual analysis that allows researchers to analyse company sentiment better or even uncover possible fraud.
Despite this information explosion, however, stock markets don't seem much more efficient than in the pre-internet era. There are several reasons for this.