A problem with the escort distribution representation of nonextensive   statistical mechanics
  It is pointed out that the Tsallis entropy functional represented in terms of the escort distribution is not concave of the entropic index $q$ is less than unity. It is emphasized that the escort distribution is a secondary object calculated from the basic original distribution. 
Sumiyoshi Abe (College of Science and Technology, Nihon University,   Funabashi, Chiba, Japan)