Efektywność informacyjna a zachowanie cen akcji tworzących indeks WIG20

This article deals with problem of informational efficiency of capital markets. In the first part theory of efficient capital markets created by Eugene Fama is described. The evolution of efficient capital market definition is presented and a new one is introduced. In the next part of the article proper null hypothesis is constructed and methods used to verify it are discussed. Author presents three groups of verification techniques: tests of autocorrelation, tests of randomness and unit root tests. In the third part of the text results of these statistical tests applied to prices of shares included in WIG20 index and values of this index as well are described. In the last part of article economic consequences for investors are presented.