Strong Form Market Efficiency

by Obaidullah Jan, ACA, CFA

Strong form of market efficiency is when prices already reflect both publically available information and inside information. In strong form of market efficiency, it is not possible to earn access return by any means.

Strong form of market efficiency is the strongest form of efficient market hypothesis, stronger than the semi-strong form of market efficiency and weak form of market efficiency.

When a market is strong form efficient, neither technical analysis nor fundamental analysis nor inside information can help predict future price movements.

Markets rarely exhibit the characteristics of strong form of market efficiency.


Shintaro Ishihara works at Osaka Automobiles as their chief engineer. He was working on a new advanced model of automobiles and the project was a big success. He was sure that this project will result in an increase in price so he purchased 10,000 shares of Osaka Automobiles for $25 per share. He was surprised to see that even after the news of the project being a success spread, the share price did not increase.

The market seems to be strong form efficient, because it had already adjusted Osaka Automobiles' stock price for the expected net present value of the new project. It already reflected the inside information.