Is it true that one can earn abnormal return when market is strong form efficient and it’s opposite case in other two forms?
When market is strong form efficient, neither public nor insider information can bring abnormal return. Fortunately even most liquid markets are not in absolute strong form efficiency.
I agree with Flashback, strong form efficient is the idealistic view which means all information is available to everyone at exactly the same time so you CAN NOT make abnormal returns in a strong form efficient market.