What concept describes a market where prices reflect all forms of information, both public and private?

The concept that describes a market where prices reflect all forms of information, both public and private, is known as strong form efficiency. In the context of the Efficient Market Hypothesis (EMH), strong form efficiency asserts that all information—regardless of whether it is publicly available or privately held—is fully accounted for in stock prices. This suggests that even insider information would not give any investor an advantage in generating excess returns, as the market has already integrated all relevant information into asset prices.

This understanding of strong form efficiency implies that in such a market, no one can consistently achieve higher returns than the market average because all information, including that which is not publicly accessible, is already reflected in stock prices. This stands in contrast to the other forms of market efficiency, including weak form and semi-strong form, which only account for certain types of information, such as historical prices or publicly available information, respectively. Therefore, strong form efficiency represents the most comprehensive level of market efficiency.