A Statistical Measure of Complexity
  A measure of complexity based on a probabilistic description of physical systems is proposed. This measure incorporates the main features of the intuitive notion of such a magnitude. It can be applied to many physical situations and to different descriptions of a given system. Moreover, the calculation of its value does not require a considerable computational effort in many cases of physical interest. 
Ricardo Lopez-Ruiz, Hector Mancini and Xavier Calbet