In short, it is important to remember that psychological weapons of mass persuasion do not need to be based on highly accurate models, nor do they require huge effects across the population in order to have the ability to undermine the democratic process. In addition, we are only seeing a fraction of the data, which means that scientific research may well be underestimating the influence of these tools. For example, most academic studies use self-reported survey experiments, which do not always accurately simulate the true social dynamics in which online news consumption takes place. Even when Facebook downplayed the importance of the echo chamber effect in their own Science study, the data was based on a tiny snapshot of users (i.e. those who declared their political ideology or about 4% of the total Facebook population). Furthermore, predictive analytics companies do not go through ethical review boards or run highly controlled studies using one or two messages at a time. Instead, they spend millions on testing thirty to forty thousand messages a day across many different audiences, fine-tuning their algorithms, refining their messages, and so on.
Needull in a haystack 
Fantastic post. Thanks for sharing!!