the theoretical relationship between informational efficiency and efficiency in the assignment is reviewed in this document. two improvements are proposed with respect to the traditional empirical methodology that is currently used to test market efficiency in the weak form. the first one is to calculate the statistic to measure efficiency dynamically. this strategy enriches the analysis and allows the reader to define intervals with different degrees of efficiency in the same market. the second one is an efficiency measure based upon copulas, which are robust in accommodating both non normality and non linearity (common features observed in financial data).