The only way you can consistently make money is by knowing things others do not (e.g., insider trading) or by taking advantage of structural problems or inefficiencies in the trading platform (e.g., high frequency trading).
I do believe that insider trading is rampant. I've seen many occasions where a large corporate announcement sends a stock up or down, but hours before, you can see the price of the stock slowly slide in the direction. Obviously a certain amount of that may be random/explainable, but I've seen it a lot and my intuition says more is going on. This also seems relatively easy to quantitatively measure, I'd love to see a real analysis of it.
I do believe that insider trading is rampant. I've seen many occasions where a large corporate announcement sends a stock up or down, but hours before, you can see the price of the stock slowly slide in the direction. Obviously a certain amount of that may be random/explainable, but I've seen it a lot and my intuition says more is going on. This also seems relatively easy to quantitatively measure, I'd love to see a real analysis of it.