Strong-form efficient market

PrepNuggets

The highest level of market efficiency is the strong-form market efficiency.  In such a market, security prices fully reflect both public and private information.  So by definition, a market that is strong-form efficient is also semi-strong and weak-form efficient.  This implies that even insiders with material private information would not be able to earn abnormal returns, as the prices already fully reflect the implications of the insider information.  However, this is not likely because given the prohibition on insider trading in most markets, it would be unrealistic to expect markets to reflect all private information.  Evidence suggests that markets are not strong-form efficient.

Compare: Weak-form efficient market hypothesis, Semi-strong-form efficient market