Zero correlation is consistent with the random-walk hypothesis. Runs tests examine the sign of price changes, or yields, during a specified sample period. If price changes are independent, the expected number of runs can be calculated. The actual number of runs can be compared with the expected in order to determine the dependence in price changes. The test of semi-strong form of the EMH, event study, analyses the behaviour of a security's price around the time of a significant event such as the public announcement of the company's profit or dividend.
Most studies use market model as a basis for estimating the normal rate of return on a security.
It is usually not possible to determine when inside information became available to insiders. Therefore, event-study methodologe is inappropriate. As a result, the typical strong-form test has involved measuring whether investors such as managers of mutual funds, who might be assumed to have access to private information, can achieve positive abnormal returns. This type of test must be regarded as, at best, an indirect test of strong-form efficiency. However strong-form efficiency seems unlikely.