In other words, fundamental analysis is of no use. The Strong form. It asserts that all information is fully reflected in securities prices. In other words, even insider information is of no use. In reality, markets are neither perfectly efficient nor completely inefficient.
All markets are efficient to a certain extent, some more so than others.
In markets with substantial impairments of efficiency, more knowledgeable investors can strive to outperform less knowledgeable ones. The efficient market debate plays an important role in the decision between active and passive investing. Active managers argue that less efficient markets provide the opportunity for outperformance by skillful managers. However, its important to realize that a majority of active managers in a given market will underperform the appropriate benchmark in the long run whether markets are or are not efficient. This is because active management is a zero-sum game in which the only way a participant can profit is for another less fortunate active participant to lose.