Strong Form Efficiency
The strongest version of market efficiency. It states all information in a market, whether public or private, is accounted for in a stock price. Not even insider information could give an investor the advantage.
Investopedia Commentary
This degree of market efficiency implies that profits exceeding normal returns cannot be made, regardless of the amount of research or information investors have access to.
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What Is Market Efficiency?
See also: Efficient Market Hypothesis, Fundamental Analysis, Random Walk Theory, Semi-Strong Form Efficiency, Technical Analysis, Weak Form Efficiency