Productivity Dispersion: Facts, Theory, and Implications
  We study productivity dispersions across workers, firms and industrial sectors. Empirical study of the Japanese data shows that they all obey the Pareto law, and also that the Pareto index decreases with the level of aggregation. In order to explain these two stylized facts, we propose a theoretical framework built upon the basic principle of statistical physics. In this framework, we employ the concept of superstatistics which accommodates fluctuations of aggregate demand. 
Hideaki Aoyama, Hiroshi Yoshikawa, Hiroshi Iyetomi and Yoshi Fujiwara