Difference in EMH

Hello, It may appear like an easy topic but im having hard time understanding the differences between all the form of efficient markets. In weak form, we assumes that all market data (price and volume data history) is already reflected in security prices : technical analysis doesn’t work, but you can still get better returns by using fundamental analysis. In semi-strong form , it contends that all public (market + non market) data are already reflected in security prices : neither fundamental nor technical analysis will yield superior returns. You need inside information to get superior returns.

In strong form , public and non public informations are reflected in stock prices. There is no information that is known or knowable (including inside information) that will yield superior investment returns. My question is : what is the difference between market data (weak form) and public data (semi strong forum) ? Weak form of market seems to me very like semi-strong form. Thank you !

Put very, very simply - public data is what you pay a research analyst to find and make sense of. All fundamental research involves culling through public data to try to identify secular shifts/trends, temporarily undervalued companies, global macro crap, etc. All the stuff you won’t find reflected in a stock’s chart.

That’s basically it.

To piggyback on STL’s answer, public data would include such things as annual reports, press releases, articles in industry publications, and the like.