Yeah this is true. In almost every technical Analysis class you would have attended this is the day 1 lesson that you get. That there are some monkeys who feel that market is a random walk theory. But you know the hypothesis of random walk theory? It doesn't says market moves randomly it says you cannot predict it using past data and two things are different. It says one cannot outperform the market without assuming "additional risk" this risk is called un systematic often referred to as Beta. Trader doesn't only predicts the direction of the market but along with that ascertains the risk of that trade and reward which he is willing to take. It's this difference of risk and return hypothesis which helps a person make money. Moreover there is this one study which you are talking about alternatively there are hundreds of studies which say markets are predictable. So just calculate accordingly.