The is gain advocated by many researchers namely Friend,

The efficient market hypothesis essentially explains that stock prices
are truly representative of all the available information and any new
information being readily reflective of the share price (Richard & Witt, 1979). Various tests of
efficient market hypothesis are conducted on the assumption of zero transaction
cost, no taxation, and free access to the availability of information for all
parties involved in the process and contract between them regarding the
ramification of information for security prices. It is not possible to test
efficient market hypotheses directly as there would be a need to know market
predicted net operational cash flows and predicted the average required rate of
return for all the future time period. The researcher would need to know all
the information available regarding the stock and the way information is
reflected in stock price. A great deal of evidence supports the three forms
i.e., weak, semi-strong and strong form. The weak form of the efficient market
hypothesis states the extent to which stock prices can be used to predict
future price pattern. A great degree of evidence suggests that such pattern
cannot predict the future. Semi-strong form attempts to explore the extent to
which share prices fully reflect all the publicly available information. This
assumption has been supported by Fama, Fisher, Jensen and Roll. Investors
predict and react to the publicly available information as to the stock price
to get any deviation from equilibrium market values. Whereas strong form is
designed to explore whether share prices are truly representative of all the
information. The hypothesis is gain advocated by many researchers namely
Friend, Brown, Herman etc. various other studies find that stock market
professionals identified all the managers of unit trusts won’t be able to earn
a return greater than the return expected at particular market risk. Though
some evidence has also been found against specialists and corporate insiders
which predicts that corporate insiders have exclusive access to the information
which equips them to earn future returns (Richard & Witt, 1979).