The Efficient Market Hypothesis is a bit of a joke when you think about it, how can one ever know that every bit of information is reflected via price? One might argue every
known bit of information is reflected in the price, but known to who?
There was a discussion on this recently by the 'founder' of the theory (Fama) and probably the biggest name in Behavioural Economics (Thaler) -
Basically you cannot ever test the Hypothesis, so it is pretty worthless. That said, if you believe that all information you need to know is contained in the price..... Well, then one can study price and use that to determine likely future moves and ignore everything else...